Re: [Xen-devel] [PATCH v2 1/3] x86: also allow REP STOS emulation acceleration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.01.15 at 11:56, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 09/01/15 10:27, Jan Beulich wrote:
>> While the REP MOVS acceleration appears to have helped qemu-traditional
>> based guests, qemu-upstream (or really the respective video BIOSes)
>> doesn't appear to benefit from that. Instead the acceleration added
>> here provides a visible performance improvement during very early HVM
>> guest boot.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> v2: fix asm() constraints in hvmemul_rep_stos(), as pointed out by
>>     Andrew. Add output operand telling the compiler that "buf" is being
>>     written.
> 
> Is writing buf wise? it looks like you will xfree() a wild pointer, and
> appears to interfere the "buf != p_data" logic.

Perhaps the textual description was a little ambiguous, but the code
is not: It's not the variable "buf" that gets written, but buf[] in its
entirety.

Jan


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