> -----Original Message-----
> From: Jan Beulich [mailto:jbeul...@suse.com]
> Sent: 09 August 2018 09:02
> To: xen-devel <xen-devel@lists.xenproject.org>
> Cc: Andrew Cooper <andrew.coop...@citrix.com>; Paul Durrant
> <paul.durr...@citrix.com>; George Dunlap <george.dun...@citrix.com>
> Subject: [PATCH RFC] x86/HVM: meet xentrace's expectations on emulation
> event data
>
> According to the logic in hvm_mmio_assist_process(), 64 bits of data are
> expected with 64-bit addresses, and 32 bits of data with 32-bit ones. I
> don't think this is very reasonable, but I'm also not going to touch the
> consumer side, the more that it is anyway not very helpful for the code
> here to only ever supply 32 bits of data (despite the field being 64
> bits wide, and having been even in the 32-bit days of Xen).
I suspect the data field was 64 bits so it could hold addresses, and no-one
thought about 64 bits of immediate data (which of course you can only get with
MMIO) whereas you can have 64-bit addresses even with PIO. Anyway the change
LGTM...
>
> Signed-off-by: Jan Beulich <jbeul...@suse.com>
Reviewed-by: Paul Durrant <paul.durr...@citrix.com>
> ---
> RFC: Untested; solely based on the observation of "(no data)" in a trace
> where it was entirely unclear why no data would have been available.
> I just so happened that the guest had more than 4Gb of memory, and
> hence addresses were not representable as 32-bit values.
>
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -30,7 +30,7 @@ struct hvmemul_cache
> static void hvmtrace_io_assist(const ioreq_t *p)
> {
> unsigned int size, event;
> - unsigned char buffer[12];
> + unsigned char buffer[16];
>
> if ( likely(!tb_init_done) )
> return;
> @@ -47,8 +47,11 @@ static void hvmtrace_io_assist(const ior
>
> if ( !p->data_is_ptr )
> {
> - *(uint32_t *)&buffer[size] = p->data;
> - size += 4;
> + if ( size == 4 )
> + *(uint32_t *)&buffer[size] = p->data;
> + else
> + *(uint64_t *)&buffer[size] = p->data;
> + size *= 2;
> }
>
> trace_var(event, 0/*!cycles*/, size, buffer);
>
>
>
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