| Message ID | df4e14ad-acd9-151e-f4a1-9cab24063b83@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
On Fri, Feb 24, 2017 at 01:14:09AM +0800, Yongji Xie wrote: > on 2017/2/24 0:15, Paolo Bonzini wrote: > > > > > On 23/02/2017 17:08, Peter Maydell wrote: > > > On 23 February 2017 at 15:58, Paolo Bonzini <pbonzini@redhat.com> wrote: > > > > However, DEVICE_NATIVE_ENDIAN would have to be paired with tswap, which > > > > the current code does not do, hence the bug. To have no swap at all, > > > > you'd need DEVICE_HOST_ENDIAN. > > > Yes, I agree that the current ramdevice code has this bug (and > > > that we can fix it by any of the various options). > > Good. :) > > > > > > > AIUI what we want for this VFIO case is "when the guest does > > > > > a 32-bit write of 0x12345678 then the bytes are 0x12 0x34 0x56 0x78 > > > > > regardless of whether TARGET_BIG_ENDIAN or not". > > > > No, I don't think so. This is not specific to VFIO. You can do it with > > > > any device, albeit VFIO is currently the only one using ramd regions. > > > The commit message in the patch that started this thread off > > > says specifically that "VFIO PCI device is little endian". > > > Is that wrong? > > Yes, I think it's a red herring. Hence my initial confusion, when I > > asked "would Yongji's patch just work if it used DEVICE_BIG_ENDIAN and > > beNN_to_cpu/cpu_to_beNN". > > > > Thank you for the great discussion. I have a better understanding of the > endianness now.:-) > > And for the commit message, I was wrong to assume the same endianness > as vfio. That's my fault. This bug should happen when target and host > endianness are different regardless of the device endianness. > > To fix it, introducing DEVICE_HOST_ENDIAN for the ram device seems to be > more reasonable than other ways. I think I'll update the patch with this > way. I think this is basically the right approach, with the only caveat being whether we want to call it "host endian" or something else. > diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h > index bd15853..eef74df 100644 > --- a/include/exec/cpu-common.h > +++ b/include/exec/cpu-common.h > @@ -36,6 +36,12 @@ enum device_endian { > DEVICE_LITTLE_ENDIAN, > }; > > +#if defined(HOST_WORDS_BIGENDIAN) > +#define DEVICE_HOST_ENDIAN DEVICE_BIG_ENDIAN > +#else > +#define DEVICE_HOST_ENDIAN DEVICE_LITTLE_ENDIAN > +#endif > + > /* address in the RAM (different from a physical address) */ > #if defined(CONFIG_XEN_BACKEND) > typedef uint64_t ram_addr_t; > diff --git a/memory.c b/memory.c > index ed8b5aa..17cfada 100644 > --- a/memory.c > +++ b/memory.c > @@ -1180,7 +1180,7 @@ static void memory_region_ram_device_write(void > *opaque, hwaddr addr, > static const MemoryRegionOps ram_device_mem_ops = { > .read = memory_region_ram_device_read, > .write = memory_region_ram_device_write, > - .endianness = DEVICE_NATIVE_ENDIAN, > + .endianness = DEVICE_HOST_ENDIAN, > .valid = { > .min_access_size = 1, > .max_access_size = 8, > > Thanks, > Yongji >
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h index bd15853..eef74df 100644 --- a/include/exec/cpu-common.h +++ b/include/exec/cpu-common.h @@ -36,6 +36,12 @@ enum device_endian { DEVICE_LITTLE_ENDIAN, }; +#if defined(HOST_WORDS_BIGENDIAN) +#define DEVICE_HOST_ENDIAN DEVICE_BIG_ENDIAN +#else +#define DEVICE_HOST_ENDIAN DEVICE_LITTLE_ENDIAN +#endif + /* address in the RAM (different from a physical address) */ #if defined(CONFIG_XEN_BACKEND) typedef uint64_t ram_addr_t; diff --git a/memory.c b/memory.c index ed8b5aa..17cfada 100644 --- a/memory.c +++ b/memory.c @@ -1180,7 +1180,7 @@ static void memory_region_ram_device_write(void *opaque, hwaddr addr, static const MemoryRegionOps ram_device_mem_ops = { .read = memory_region_ram_device_read, .write = memory_region_ram_device_write, - .endianness = DEVICE_NATIVE_ENDIAN, + .endianness = DEVICE_HOST_ENDIAN, .valid = { .min_access_size = 1,