| Message ID | 20220525124944.2613333-1-farosas@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | KVM: PPC: Align pt_regs in kvm_vcpu_arch structure | expand |
Hi, Fabiano. On 5/25/22 09:49, Fabiano Rosas wrote: > The H_ENTER_NESTED hypercall receives as second parameter the address > of a region of memory containing the values for the nested guest > privileged registers. We currently use the pt_regs structure contained > within kvm_vcpu_arch for that end. > > Most hypercalls that receive a memory address expect that region to > not cross a 4k page boundary. We would want H_ENTER_NESTED to follow > the same pattern so this patch ensures the pt_regs structure sits > within a page. > > Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com> Is it necessary to explain in the commit message that even though the second parameter needs to be 4k-aligned, we're aligning pt_regs to 512 bytes so it can be placed within a 4k boundary because its size is below 512 bytes? The natural thinking would be aligning it to 4k bytes, which would punch a huge hole in kvm_vcpu_arch. I think having the explanation of why 512 vs. 4k is worthwhile mentioning. > --- > arch/powerpc/include/asm/kvm_host.h | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h > index faf301d0dec0..87eba60f2920 100644 > --- a/arch/powerpc/include/asm/kvm_host.h > +++ b/arch/powerpc/include/asm/kvm_host.h > @@ -519,7 +519,11 @@ struct kvm_vcpu_arch { > struct kvmppc_book3s_shadow_vcpu *shadow_vcpu; > #endif > > - struct pt_regs regs; > + /* > + * This is passed along to the HV via H_ENTER_NESTED. Align to > + * prevent it crossing a real 4K page. > + */ > + struct pt_regs regs __aligned(512); > > struct thread_fp_state fp; >
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index faf301d0dec0..87eba60f2920 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -519,7 +519,11 @@ struct kvm_vcpu_arch { struct kvmppc_book3s_shadow_vcpu *shadow_vcpu; #endif - struct pt_regs regs; + /* + * This is passed along to the HV via H_ENTER_NESTED. Align to + * prevent it crossing a real 4K page. + */ + struct pt_regs regs __aligned(512); struct thread_fp_state fp;
The H_ENTER_NESTED hypercall receives as second parameter the address of a region of memory containing the values for the nested guest privileged registers. We currently use the pt_regs structure contained within kvm_vcpu_arch for that end. Most hypercalls that receive a memory address expect that region to not cross a 4k page boundary. We would want H_ENTER_NESTED to follow the same pattern so this patch ensures the pt_regs structure sits within a page. Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com> --- arch/powerpc/include/asm/kvm_host.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)