diff mbox series

[v2,10/19] target/riscv: remove kvm-stub.c

Message ID 20230906091647.1667171-11-dbarboza@ventanamicro.com
State New
Headers show
Series riscv: split TCG/KVM accelerators from cpu.c | expand

Commit Message

Daniel Henrique Barboza Sept. 6, 2023, 9:16 a.m. UTC
This file is not needed for some time now. All the stubs implemented in
it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
kvm_enabled()' blocks that the compiler will rip it out in non-KVM
builds.

We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
All stubs are implemented as g_asserted_not_reached(), meaning that we
won't support them in non-KVM builds. This is done by other kvm headers
like kvm_arm.h and kvm_ppc.h.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/kvm-stub.c  | 30 ------------------------------
 target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
 target/riscv/meson.build |  2 +-
 3 files changed, 32 insertions(+), 31 deletions(-)
 delete mode 100644 target/riscv/kvm-stub.c

Comments

Philippe Mathieu-Daudé Sept. 6, 2023, 10:23 a.m. UTC | #1
On 6/9/23 11:16, Daniel Henrique Barboza wrote:
> This file is not needed for some time now. All the stubs implemented in
> it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
> kvm_enabled()' blocks that the compiler will rip it out in non-KVM
> builds.
> 
> We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
> All stubs are implemented as g_asserted_not_reached(), meaning that we
> won't support them in non-KVM builds. This is done by other kvm headers
> like kvm_arm.h and kvm_ppc.h.

Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?

> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>   target/riscv/kvm-stub.c  | 30 ------------------------------
>   target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
>   target/riscv/meson.build |  2 +-
>   3 files changed, 32 insertions(+), 31 deletions(-)
>   delete mode 100644 target/riscv/kvm-stub.c


> diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
> index f6501e68e2..c9ecd9a967 100644
> --- a/target/riscv/kvm_riscv.h
> +++ b/target/riscv/kvm_riscv.h
> @@ -19,6 +19,7 @@
>   #ifndef QEMU_KVM_RISCV_H
>   #define QEMU_KVM_RISCV_H
>   
> +#ifdef CONFIG_KVM
>   void kvm_riscv_cpu_add_kvm_properties(Object *obj);

At a glance kvm_riscv_cpu_add_kvm_properties() is.
Keep the prototype declared (before #ifdef CONFIG_KVM) is enough for the
compiler to elide it.

>   void kvm_riscv_reset_vcpu(RISCVCPU *cpu);
>   void kvm_riscv_set_irq(RISCVCPU *cpu, int irq, int level);
> @@ -27,5 +28,35 @@ void kvm_riscv_aia_create(MachineState *machine, uint64_t group_shift,
>                             uint64_t aplic_base, uint64_t imsic_base,
>                             uint64_t guest_num);
>   void riscv_kvm_aplic_request(void *opaque, int irq, int level);
> +#else
> +static inline void kvm_riscv_cpu_add_kvm_properties(Object *obj)
> +{
> +    g_assert_not_reached();
> +}
> +
> +static inline void kvm_riscv_reset_vcpu(RISCVCPU *cpu)
> +{
> +    g_assert_not_reached();
> +}
> +
> +static inline void kvm_riscv_set_irq(RISCVCPU *cpu, int irq, int level)
> +{
> +    g_assert_not_reached();
> +}
> +
> +static inline void kvm_riscv_aia_create(MachineState *machine,
> +                          uint64_t group_shift, uint64_t aia_irq_num,
> +                          uint64_t aia_msi_num, uint64_t aplic_base,
> +                          uint64_t imsic_base, uint64_t guest_num)
> +{
> +    g_assert_not_reached();
> +}
> +
> +static inline void riscv_kvm_aplic_request(void *opaque, int irq, int level)
> +{
> +    g_assert_not_reached();
> +}
> +
> +#endif /* CONFIG_KVM */
Andrew Jones Sept. 11, 2023, 7:49 a.m. UTC | #2
On Wed, Sep 06, 2023 at 12:23:19PM +0200, Philippe Mathieu-Daudé wrote:
> On 6/9/23 11:16, Daniel Henrique Barboza wrote:
> > This file is not needed for some time now. All the stubs implemented in
> > it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
> > kvm_enabled()' blocks that the compiler will rip it out in non-KVM
> > builds.
> > 
> > We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
> > All stubs are implemented as g_asserted_not_reached(), meaning that we
> > won't support them in non-KVM builds. This is done by other kvm headers
> > like kvm_arm.h and kvm_ppc.h.
> 
> Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?

Yes, I think your earlier suggestion that we always invoke kvm functions
from non-kvm files with a kvm_enabled() guard makes sense.

> 
> > Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> > ---
> >   target/riscv/kvm-stub.c  | 30 ------------------------------
> >   target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
> >   target/riscv/meson.build |  2 +-
> >   3 files changed, 32 insertions(+), 31 deletions(-)
> >   delete mode 100644 target/riscv/kvm-stub.c
> 
> 
> > diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
> > index f6501e68e2..c9ecd9a967 100644
> > --- a/target/riscv/kvm_riscv.h
> > +++ b/target/riscv/kvm_riscv.h
> > @@ -19,6 +19,7 @@
> >   #ifndef QEMU_KVM_RISCV_H
> >   #define QEMU_KVM_RISCV_H
> > +#ifdef CONFIG_KVM
> >   void kvm_riscv_cpu_add_kvm_properties(Object *obj);
> 
> At a glance kvm_riscv_cpu_add_kvm_properties() is.
> Keep the prototype declared (before #ifdef CONFIG_KVM) is enough for the
> compiler to elide it.

Yes, when building without CONFIG_KVM enabled it's actually better to not
have the stubs, since the compiler will catch an unguarded kvm function
call (assuming the kvm function is defined in a file which is only built
with CONFIG_KVM).

Unfortunately we don't have anything to protect developers from forgetting
the kvm_enabled() guard when building a QEMU which supports both TCG and
KVM. We could try to remember to put 'assert(kvm_enabled())' at the start
of each of these types of functions. It looks like mips does that for a
couple functions.

Thanks,
drew
Andrew Jones Sept. 11, 2023, 9:04 a.m. UTC | #3
On Mon, Sep 11, 2023 at 09:49:06AM +0200, Andrew Jones wrote:
> On Wed, Sep 06, 2023 at 12:23:19PM +0200, Philippe Mathieu-Daudé wrote:
> > On 6/9/23 11:16, Daniel Henrique Barboza wrote:
> > > This file is not needed for some time now. All the stubs implemented in
> > > it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
> > > kvm_enabled()' blocks that the compiler will rip it out in non-KVM
> > > builds.
> > > 
> > > We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
> > > All stubs are implemented as g_asserted_not_reached(), meaning that we
> > > won't support them in non-KVM builds. This is done by other kvm headers
> > > like kvm_arm.h and kvm_ppc.h.
> > 
> > Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?
> 
> Yes, I think your earlier suggestion that we always invoke kvm functions
> from non-kvm files with a kvm_enabled() guard makes sense.
> 
> > 
> > > Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> > > ---
> > >   target/riscv/kvm-stub.c  | 30 ------------------------------
> > >   target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
> > >   target/riscv/meson.build |  2 +-
> > >   3 files changed, 32 insertions(+), 31 deletions(-)
> > >   delete mode 100644 target/riscv/kvm-stub.c
> > 
> > 
> > > diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
> > > index f6501e68e2..c9ecd9a967 100644
> > > --- a/target/riscv/kvm_riscv.h
> > > +++ b/target/riscv/kvm_riscv.h
> > > @@ -19,6 +19,7 @@
> > >   #ifndef QEMU_KVM_RISCV_H
> > >   #define QEMU_KVM_RISCV_H
> > > +#ifdef CONFIG_KVM
> > >   void kvm_riscv_cpu_add_kvm_properties(Object *obj);
> > 
> > At a glance kvm_riscv_cpu_add_kvm_properties() is.
> > Keep the prototype declared (before #ifdef CONFIG_KVM) is enough for the
> > compiler to elide it.
> 
> Yes, when building without CONFIG_KVM enabled it's actually better to not
> have the stubs, since the compiler will catch an unguarded kvm function
> call (assuming the kvm function is defined in a file which is only built
> with CONFIG_KVM).
> 
> Unfortunately we don't have anything to protect developers from forgetting
> the kvm_enabled() guard when building a QEMU which supports both TCG and
> KVM. We could try to remember to put 'assert(kvm_enabled())' at the start
> of each of these types of functions. It looks like mips does that for a
> couple functions.

Eh, ignore this suggestion. We don't need asserts, because we have CI. As
long as our CI does a CONFIG_KVM=n build and all KVM functions are in kvm-
only files, then we'll always catch calls of KVM functions which are
missing their kvm_enabled() guards.

Thanks,
drew
Daniel Henrique Barboza Sept. 11, 2023, 12:23 p.m. UTC | #4
On 9/11/23 06:04, Andrew Jones wrote:
> On Mon, Sep 11, 2023 at 09:49:06AM +0200, Andrew Jones wrote:
>> On Wed, Sep 06, 2023 at 12:23:19PM +0200, Philippe Mathieu-Daudé wrote:
>>> On 6/9/23 11:16, Daniel Henrique Barboza wrote:
>>>> This file is not needed for some time now. All the stubs implemented in
>>>> it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
>>>> kvm_enabled()' blocks that the compiler will rip it out in non-KVM
>>>> builds.
>>>>
>>>> We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
>>>> All stubs are implemented as g_asserted_not_reached(), meaning that we
>>>> won't support them in non-KVM builds. This is done by other kvm headers
>>>> like kvm_arm.h and kvm_ppc.h.
>>>
>>> Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?
>>
>> Yes, I think your earlier suggestion that we always invoke kvm functions
>> from non-kvm files with a kvm_enabled() guard makes sense.
>>
>>>
>>>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>>>> ---
>>>>    target/riscv/kvm-stub.c  | 30 ------------------------------
>>>>    target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
>>>>    target/riscv/meson.build |  2 +-
>>>>    3 files changed, 32 insertions(+), 31 deletions(-)
>>>>    delete mode 100644 target/riscv/kvm-stub.c
>>>
>>>
>>>> diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
>>>> index f6501e68e2..c9ecd9a967 100644
>>>> --- a/target/riscv/kvm_riscv.h
>>>> +++ b/target/riscv/kvm_riscv.h
>>>> @@ -19,6 +19,7 @@
>>>>    #ifndef QEMU_KVM_RISCV_H
>>>>    #define QEMU_KVM_RISCV_H
>>>> +#ifdef CONFIG_KVM
>>>>    void kvm_riscv_cpu_add_kvm_properties(Object *obj);
>>>
>>> At a glance kvm_riscv_cpu_add_kvm_properties() is.
>>> Keep the prototype declared (before #ifdef CONFIG_KVM) is enough for the
>>> compiler to elide it.
>>
>> Yes, when building without CONFIG_KVM enabled it's actually better to not
>> have the stubs, since the compiler will catch an unguarded kvm function
>> call (assuming the kvm function is defined in a file which is only built
>> with CONFIG_KVM).
>>
>> Unfortunately we don't have anything to protect developers from forgetting
>> the kvm_enabled() guard when building a QEMU which supports both TCG and
>> KVM. We could try to remember to put 'assert(kvm_enabled())' at the start
>> of each of these types of functions. It looks like mips does that for a
>> couple functions.
> 
> Eh, ignore this suggestion. We don't need asserts, because we have CI. As
> long as our CI does a CONFIG_KVM=n build and all KVM functions are in kvm-
> only files, then we'll always catch calls of KVM functions which are
> missing their kvm_enabled() guards.

So, to sum up, get rid of the 'g_assert_not_reached()' stubs since they should
be cropped by well placed kvm_enabled() calls in the code and, if that's not
the case, a non-KVM build failure will let us know that there's something wrong.

I can live with that. It's less code to deal with in the header as well. Thanks,


Daniel


> 
> Thanks,
> drew
Daniel Henrique Barboza Sept. 12, 2023, 10:48 a.m. UTC | #5
On 9/11/23 09:23, Daniel Henrique Barboza wrote:
> 
> 
> On 9/11/23 06:04, Andrew Jones wrote:
>> On Mon, Sep 11, 2023 at 09:49:06AM +0200, Andrew Jones wrote:
>>> On Wed, Sep 06, 2023 at 12:23:19PM +0200, Philippe Mathieu-Daudé wrote:
>>>> On 6/9/23 11:16, Daniel Henrique Barboza wrote:
>>>>> This file is not needed for some time now. All the stubs implemented in
>>>>> it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
>>>>> kvm_enabled()' blocks that the compiler will rip it out in non-KVM
>>>>> builds.
>>>>>
>>>>> We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
>>>>> All stubs are implemented as g_asserted_not_reached(), meaning that we
>>>>> won't support them in non-KVM builds. This is done by other kvm headers
>>>>> like kvm_arm.h and kvm_ppc.h.
>>>>
>>>> Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?
>>>
>>> Yes, I think your earlier suggestion that we always invoke kvm functions
>>> from non-kvm files with a kvm_enabled() guard makes sense.
>>>
>>>>
>>>>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>>>>> ---
>>>>>    target/riscv/kvm-stub.c  | 30 ------------------------------
>>>>>    target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
>>>>>    target/riscv/meson.build |  2 +-
>>>>>    3 files changed, 32 insertions(+), 31 deletions(-)
>>>>>    delete mode 100644 target/riscv/kvm-stub.c
>>>>
>>>>
>>>>> diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
>>>>> index f6501e68e2..c9ecd9a967 100644
>>>>> --- a/target/riscv/kvm_riscv.h
>>>>> +++ b/target/riscv/kvm_riscv.h
>>>>> @@ -19,6 +19,7 @@
>>>>>    #ifndef QEMU_KVM_RISCV_H
>>>>>    #define QEMU_KVM_RISCV_H
>>>>> +#ifdef CONFIG_KVM
>>>>>    void kvm_riscv_cpu_add_kvm_properties(Object *obj);
>>>>
>>>> At a glance kvm_riscv_cpu_add_kvm_properties() is.
>>>> Keep the prototype declared (before #ifdef CONFIG_KVM) is enough for the
>>>> compiler to elide it.
>>>
>>> Yes, when building without CONFIG_KVM enabled it's actually better to not
>>> have the stubs, since the compiler will catch an unguarded kvm function
>>> call (assuming the kvm function is defined in a file which is only built
>>> with CONFIG_KVM).
>>>
>>> Unfortunately we don't have anything to protect developers from forgetting
>>> the kvm_enabled() guard when building a QEMU which supports both TCG and
>>> KVM. We could try to remember to put 'assert(kvm_enabled())' at the start
>>> of each of these types of functions. It looks like mips does that for a
>>> couple functions.
>>
>> Eh, ignore this suggestion. We don't need asserts, because we have CI. As
>> long as our CI does a CONFIG_KVM=n build and all KVM functions are in kvm-
>> only files, then we'll always catch calls of KVM functions which are
>> missing their kvm_enabled() guards.
> 
> So, to sum up, get rid of the 'g_assert_not_reached()' stubs since they should
> be cropped by well placed kvm_enabled() calls in the code and, if that's not
> the case, a non-KVM build failure will let us know that there's something wrong.
> 
> I can live with that. It's less code to deal with in the header as well. Thanks,


I changed my mind after talking with Michael in this thread:

https://lists.gnu.org/archive/html/qemu-devel/2023-09/msg02567.html


There are differences in how gcc and clang (and probably other toolchains) behave
when choosing to crop code gated with 'if (kvm_enabled && something)'. It is
better to have stubs for all KVM functions to avoid relying on compiler behavior.

We should keep the stubs in this patch as is. Thanks,


Daniel


> 
> 
> Daniel
> 
> 
>>
>> Thanks,
>> drew
Philippe Mathieu-Daudé Sept. 12, 2023, 11:15 a.m. UTC | #6
On 12/9/23 12:48, Daniel Henrique Barboza wrote:
> On 9/11/23 09:23, Daniel Henrique Barboza wrote:
>> On 9/11/23 06:04, Andrew Jones wrote:
>>> On Mon, Sep 11, 2023 at 09:49:06AM +0200, Andrew Jones wrote:
>>>> On Wed, Sep 06, 2023 at 12:23:19PM +0200, Philippe Mathieu-Daudé wrote:
>>>>> On 6/9/23 11:16, Daniel Henrique Barboza wrote:
>>>>>> This file is not needed for some time now. All the stubs 
>>>>>> implemented in
>>>>>> it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 
>>>>>> 'if
>>>>>> kvm_enabled()' blocks that the compiler will rip it out in non-KVM
>>>>>> builds.
>>>>>>
>>>>>> We'll also add non-KVM stubs for all functions declared in 
>>>>>> kvm_riscv.h.
>>>>>> All stubs are implemented as g_asserted_not_reached(), meaning 
>>>>>> that we
>>>>>> won't support them in non-KVM builds. This is done by other kvm 
>>>>>> headers
>>>>>> like kvm_arm.h and kvm_ppc.h.
>>>>>
>>>>> Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?
>>>>
>>>> Yes, I think your earlier suggestion that we always invoke kvm 
>>>> functions
>>>> from non-kvm files with a kvm_enabled() guard makes sense.
>>>>
>>>>>
>>>>>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>>>>>> ---
>>>>>>    target/riscv/kvm-stub.c  | 30 ------------------------------
>>>>>>    target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
>>>>>>    target/riscv/meson.build |  2 +-
>>>>>>    3 files changed, 32 insertions(+), 31 deletions(-)
>>>>>>    delete mode 100644 target/riscv/kvm-stub.c
>>>>>
>>>>>
>>>>>> diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
>>>>>> index f6501e68e2..c9ecd9a967 100644
>>>>>> --- a/target/riscv/kvm_riscv.h
>>>>>> +++ b/target/riscv/kvm_riscv.h
>>>>>> @@ -19,6 +19,7 @@
>>>>>>    #ifndef QEMU_KVM_RISCV_H
>>>>>>    #define QEMU_KVM_RISCV_H
>>>>>> +#ifdef CONFIG_KVM
>>>>>>    void kvm_riscv_cpu_add_kvm_properties(Object *obj);
>>>>>
>>>>> At a glance kvm_riscv_cpu_add_kvm_properties() is.
>>>>> Keep the prototype declared (before #ifdef CONFIG_KVM) is enough 
>>>>> for the
>>>>> compiler to elide it.
>>>>
>>>> Yes, when building without CONFIG_KVM enabled it's actually better 
>>>> to not
>>>> have the stubs, since the compiler will catch an unguarded kvm function
>>>> call (assuming the kvm function is defined in a file which is only 
>>>> built
>>>> with CONFIG_KVM).
>>>>
>>>> Unfortunately we don't have anything to protect developers from 
>>>> forgetting
>>>> the kvm_enabled() guard when building a QEMU which supports both TCG 
>>>> and
>>>> KVM. We could try to remember to put 'assert(kvm_enabled())' at the 
>>>> start
>>>> of each of these types of functions. It looks like mips does that for a
>>>> couple functions.
>>>
>>> Eh, ignore this suggestion. We don't need asserts, because we have 
>>> CI. As
>>> long as our CI does a CONFIG_KVM=n build and all KVM functions are in 
>>> kvm-
>>> only files, then we'll always catch calls of KVM functions which are
>>> missing their kvm_enabled() guards.
>>
>> So, to sum up, get rid of the 'g_assert_not_reached()' stubs since 
>> they should
>> be cropped by well placed kvm_enabled() calls in the code and, if 
>> that's not
>> the case, a non-KVM build failure will let us know that there's 
>> something wrong.
>>
>> I can live with that. It's less code to deal with in the header as 
>> well. Thanks,
> 
> 
> I changed my mind after talking with Michael in this thread:
> 
> https://lists.gnu.org/archive/html/qemu-devel/2023-09/msg02567.html
> 
> 
> There are differences in how gcc and clang (and probably other 
> toolchains) behave
> when choosing to crop code gated with 'if (kvm_enabled && something)'. 
> It is
> better to have stubs for all KVM functions to avoid relying on compiler 
> behavior.
> 
> We should keep the stubs in this patch as is. Thanks,

Don't get stuck at this; get your series merged, we'll have a look
at that later, this is not important.

Regards,

Phil.
Daniel Henrique Barboza Sept. 12, 2023, 12:03 p.m. UTC | #7
On 9/12/23 08:15, Philippe Mathieu-Daudé wrote:
> On 12/9/23 12:48, Daniel Henrique Barboza wrote:
>> On 9/11/23 09:23, Daniel Henrique Barboza wrote:
>>> On 9/11/23 06:04, Andrew Jones wrote:
>>>> On Mon, Sep 11, 2023 at 09:49:06AM +0200, Andrew Jones wrote:
>>>>> On Wed, Sep 06, 2023 at 12:23:19PM +0200, Philippe Mathieu-Daudé wrote:
>>>>>> On 6/9/23 11:16, Daniel Henrique Barboza wrote:
>>>>>>> This file is not needed for some time now. All the stubs implemented in
>>>>>>> it (kvm_riscv_reset_vcpu() and kvm_riscv_set_irq()) are wrapped in 'if
>>>>>>> kvm_enabled()' blocks that the compiler will rip it out in non-KVM
>>>>>>> builds.
>>>>>>>
>>>>>>> We'll also add non-KVM stubs for all functions declared in kvm_riscv.h.
>>>>>>> All stubs are implemented as g_asserted_not_reached(), meaning that we
>>>>>>> won't support them in non-KVM builds. This is done by other kvm headers
>>>>>>> like kvm_arm.h and kvm_ppc.h.
>>>>>>
>>>>>> Aren't them also protected by kvm_enabled()? Otherwise shouldn't they?
>>>>>
>>>>> Yes, I think your earlier suggestion that we always invoke kvm functions
>>>>> from non-kvm files with a kvm_enabled() guard makes sense.
>>>>>
>>>>>>
>>>>>>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>>>>>>> ---
>>>>>>>    target/riscv/kvm-stub.c  | 30 ------------------------------
>>>>>>>    target/riscv/kvm_riscv.h | 31 +++++++++++++++++++++++++++++++
>>>>>>>    target/riscv/meson.build |  2 +-
>>>>>>>    3 files changed, 32 insertions(+), 31 deletions(-)
>>>>>>>    delete mode 100644 target/riscv/kvm-stub.c
>>>>>>
>>>>>>
>>>>>>> diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
>>>>>>> index f6501e68e2..c9ecd9a967 100644
>>>>>>> --- a/target/riscv/kvm_riscv.h
>>>>>>> +++ b/target/riscv/kvm_riscv.h
>>>>>>> @@ -19,6 +19,7 @@
>>>>>>>    #ifndef QEMU_KVM_RISCV_H
>>>>>>>    #define QEMU_KVM_RISCV_H
>>>>>>> +#ifdef CONFIG_KVM
>>>>>>>    void kvm_riscv_cpu_add_kvm_properties(Object *obj);
>>>>>>
>>>>>> At a glance kvm_riscv_cpu_add_kvm_properties() is.
>>>>>> Keep the prototype declared (before #ifdef CONFIG_KVM) is enough for the
>>>>>> compiler to elide it.
>>>>>
>>>>> Yes, when building without CONFIG_KVM enabled it's actually better to not
>>>>> have the stubs, since the compiler will catch an unguarded kvm function
>>>>> call (assuming the kvm function is defined in a file which is only built
>>>>> with CONFIG_KVM).
>>>>>
>>>>> Unfortunately we don't have anything to protect developers from forgetting
>>>>> the kvm_enabled() guard when building a QEMU which supports both TCG and
>>>>> KVM. We could try to remember to put 'assert(kvm_enabled())' at the start
>>>>> of each of these types of functions. It looks like mips does that for a
>>>>> couple functions.
>>>>
>>>> Eh, ignore this suggestion. We don't need asserts, because we have CI. As
>>>> long as our CI does a CONFIG_KVM=n build and all KVM functions are in kvm-
>>>> only files, then we'll always catch calls of KVM functions which are
>>>> missing their kvm_enabled() guards.
>>>
>>> So, to sum up, get rid of the 'g_assert_not_reached()' stubs since they should
>>> be cropped by well placed kvm_enabled() calls in the code and, if that's not
>>> the case, a non-KVM build failure will let us know that there's something wrong.
>>>
>>> I can live with that. It's less code to deal with in the header as well. Thanks,
>>
>>
>> I changed my mind after talking with Michael in this thread:
>>
>> https://lists.gnu.org/archive/html/qemu-devel/2023-09/msg02567.html
>>
>>
>> There are differences in how gcc and clang (and probably other toolchains) behave
>> when choosing to crop code gated with 'if (kvm_enabled && something)'. It is
>> better to have stubs for all KVM functions to avoid relying on compiler behavior.
>>
>> We should keep the stubs in this patch as is. Thanks,
> 
> Don't get stuck at this; get your series merged, we'll have a look
> at that later, this is not important.


Ok, so we'll simplify here and avoid the unneeded stubs for now as we initially discussed,
while making sure we're not breaking builds with --enable-debug and clang. After this
is merged we can reevaluate the best approach to take.


Thanks,


Daniel

> 
> Regards,
> 
> Phil.
diff mbox series

Patch

diff --git a/target/riscv/kvm-stub.c b/target/riscv/kvm-stub.c
deleted file mode 100644
index 4e8fc31a21..0000000000
--- a/target/riscv/kvm-stub.c
+++ /dev/null
@@ -1,30 +0,0 @@ 
-/*
- * QEMU KVM RISC-V specific function stubs
- *
- * Copyright (c) 2020 Huawei Technologies Co., Ltd
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms and conditions of the GNU General Public License,
- * version 2 or later, as published by the Free Software Foundation.
- *
- * This program is distributed in the hope it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
- * more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-#include "qemu/osdep.h"
-#include "cpu.h"
-#include "kvm_riscv.h"
-
-void kvm_riscv_reset_vcpu(RISCVCPU *cpu)
-{
-    abort();
-}
-
-void kvm_riscv_set_irq(RISCVCPU *cpu, int irq, int level)
-{
-    abort();
-}
diff --git a/target/riscv/kvm_riscv.h b/target/riscv/kvm_riscv.h
index f6501e68e2..c9ecd9a967 100644
--- a/target/riscv/kvm_riscv.h
+++ b/target/riscv/kvm_riscv.h
@@ -19,6 +19,7 @@ 
 #ifndef QEMU_KVM_RISCV_H
 #define QEMU_KVM_RISCV_H
 
+#ifdef CONFIG_KVM
 void kvm_riscv_cpu_add_kvm_properties(Object *obj);
 void kvm_riscv_reset_vcpu(RISCVCPU *cpu);
 void kvm_riscv_set_irq(RISCVCPU *cpu, int irq, int level);
@@ -27,5 +28,35 @@  void kvm_riscv_aia_create(MachineState *machine, uint64_t group_shift,
                           uint64_t aplic_base, uint64_t imsic_base,
                           uint64_t guest_num);
 void riscv_kvm_aplic_request(void *opaque, int irq, int level);
+#else
+static inline void kvm_riscv_cpu_add_kvm_properties(Object *obj)
+{
+    g_assert_not_reached();
+}
+
+static inline void kvm_riscv_reset_vcpu(RISCVCPU *cpu)
+{
+    g_assert_not_reached();
+}
+
+static inline void kvm_riscv_set_irq(RISCVCPU *cpu, int irq, int level)
+{
+    g_assert_not_reached();
+}
+
+static inline void kvm_riscv_aia_create(MachineState *machine,
+                          uint64_t group_shift, uint64_t aia_irq_num,
+                          uint64_t aia_msi_num, uint64_t aplic_base,
+                          uint64_t imsic_base, uint64_t guest_num)
+{
+    g_assert_not_reached();
+}
+
+static inline void riscv_kvm_aplic_request(void *opaque, int irq, int level)
+{
+    g_assert_not_reached();
+}
+
+#endif /* CONFIG_KVM */
 
 #endif
diff --git a/target/riscv/meson.build b/target/riscv/meson.build
index f0486183fa..3323b78b84 100644
--- a/target/riscv/meson.build
+++ b/target/riscv/meson.build
@@ -24,7 +24,7 @@  riscv_ss.add(files(
   'zce_helper.c',
   'vcrypto_helper.c'
 ))
-riscv_ss.add(when: 'CONFIG_KVM', if_true: files('kvm.c'), if_false: files('kvm-stub.c'))
+riscv_ss.add(when: 'CONFIG_KVM', if_true: files('kvm.c'))
 
 riscv_system_ss = ss.source_set()
 riscv_system_ss.add(files(