Re: [PATCH] acpi: Fix access to PM1 control and status registers

[Anthony PERARD <anthony.perard@citrix.com>]

On Thu, Jul 02, 2020 at 07:12:08AM -0400, Michael S. Tsirkin wrote:
> memory: align to min access size
> 
> If impl.min_access_size > valid.min_access_size access callbacks
> can get a misaligned access as size is increased.
> They don't expect that, let's fix it in the memory core.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> ---
> 
> 
> diff --git a/memory.c b/memory.c
> index 9200b20130..ea489ce405 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -532,6 +532,7 @@ static MemTxResult access_with_adjusted_size(hwaddr addr,
>      }
>  
>      /* FIXME: support unaligned access? */
> +    addr &= ~(access_size_min - 1);
>      access_size = MAX(MIN(size, access_size_max), access_size_min);
>      access_mask = MAKE_64BIT_MASK(0, access_size * 8);
>      if (memory_region_big_endian(mr)) {

I've tried this (and .impl.min_access_size=2) but that wasn't enough.

In the guest, I did `inb(base_addr + 1)`, but I've got back the value as
if `inb(base_addr)` was run.

The device emulation read callbacks did get addr=0 width=2, so that's
fine, but the result returned to the guest wasn't shifted. Same thing
for write access, the write value isn't shifted, so a write to the
second byte would be written to the first.

Thanks,

-- 
Anthony PERARD