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Re: [Xen-devel] [PATCH] x86/svm: Reduce vmentry latency

On 10.02.2020 13:09, Roger Pau Monné wrote:
> On Mon, Feb 10, 2020 at 11:42:06AM +0000, Andrew Cooper wrote:
>> Writing to the stack pointer in the middle of a line of pop operations is
>> specifically recommended against by the optimisation guide, and is a 
>> technique
>> used by Speculative Load Hardening to combat SpectreRSB.
>> In practice, it causes all further stack-relative accesses to block until the
>> write to the stack pointer retires, so the stack engine can get back in sync.
>> Pop into any dead register to discard %rax's value without clobbering the
>> stack engine.  Smaller compiled code, and runs faster.
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

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