On 21/02/2017 19:44, Alex Williamson wrote:
>>> In other words, would Yongji's patch just work if it used
>>> DEVICE_BIG_ENDIAN and beNN_to_cpu/cpu_to_beNN? If so, then I think the
>>> patch is okay.
>
> The part where I get lost is that if PPC64 always sets the target
> to big endian, then adjust_endianness() we will always bswap after a
> read and before a write. I don't follow how that bswap necessarily
> gets us to QEMU CPU endian such that the cpu_to_leXX/leXX_to_cpu in the
> access functions always do the right thing. I know we do this
> elsewhere in vfio, perhaps I've deferred to someone convincing me it
> was the right thing at the time, but I'm not able to derive it myself
> currently.
>
> To answer Paolo's question, if PPC64 sets TARGET_WORDS_BIGENDIAN, which
> is a compile time setting, then using DEVICE_BIG_ENDIAN would
> deterministically remove the bswap from adjust_endianness(),
And beNN_to_cpu/cpu_to_beNN would add a swap in
memory_region_ram_device_read/write, so it would work just as well.
KVM expects data in host endianness:
static inline bool kvmppc_need_byteswap(struct kvm_vcpu *vcpu)
{
return (kvmppc_get_msr(vcpu) & MSR_LE) != (MSR_KERNEL & MSR_LE);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^
endianness of the target endianness of
struct kvm_run
}
while QEMU hardcodes bigendian for DEVICE_NATIVE_ENDIAN, even if
running on PPC64LE host.
However, I'm confused as to what would happen with TCG. :( The best
thing to do, IMO, is to add a RAM device MR to pc-testdev (e.g. at 0xec)
diff --git a/hw/misc/pc-testdev.c b/hw/misc/pc-testdev.c
index b81d820..5ea444f 100644
--- a/hw/misc/pc-testdev.c
+++ b/hw/misc/pc-testdev.c
@@ -47,11 +47,13 @@ typedef struct PCTestdev {
MemoryRegion ioport;
MemoryRegion ioport_byte;
+ MemoryRegion ioport_ramd;
MemoryRegion flush;
MemoryRegion irq;
MemoryRegion iomem;
uint32_t ioport_data;
char iomem_buf[IOMEM_LEN];
+ char ioport_ramd_bytes[4];
} PCTestdev;
#define TYPE_TESTDEV "pc-testdev"
@@ -167,6 +169,10 @@ static void testdev_realizefn(DeviceState *d, Error **errp)
memory_region_init_io(&dev->ioport_byte, OBJECT(dev),
&test_ioport_byte_ops, dev,
"pc-testdev-ioport-byte", 4);
+ memory_region_init_ram_device_ptr(&dev->ioport_ramd, OBJECT(dev),
+ "pc-testdev-ioport-ramd",
+ ARRAY_SIZE(dev->ioport_ramd_bytes),
+ &dev->ioport_ramd_bytes);
memory_region_init_io(&dev->flush, OBJECT(dev), &test_flush_ops, dev,
"pc-testdev-flush-page", 4);
memory_region_init_io(&dev->irq, OBJECT(dev), &test_irq_ops, dev,
@@ -177,6 +183,7 @@ static void testdev_realizefn(DeviceState *d, Error **errp)
memory_region_add_subregion(io, 0xe0, &dev->ioport);
memory_region_add_subregion(io, 0xe4, &dev->flush);
memory_region_add_subregion(io, 0xe8, &dev->ioport_byte);
+ memory_region_add_subregion(io, 0xec, &dev->ioport_ramd);
memory_region_add_subregion(io, 0x2000, &dev->irq);
memory_region_add_subregion(mem, 0xff000000, &dev->iomem);
}
and a testcase to tests/endianness-test.c.
Paolo
