linux-kernel - Re: [PATCH] KVM/VMX: Avoid stack engine synchronization uop in __vmx_vcpu

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Message-ID: <Yw6EgFOcnCGa5hOo@google.com>
Date:   Tue, 30 Aug 2022 21:43:28 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH] KVM/VMX: Avoid stack engine synchronization uop in
 __vmx_vcpu_run

On Tue, Aug 16, 2022, Uros Bizjak wrote:
> Avoid instructions with explicit uses of the stack pointer between
> instructions that implicitly refer to it. The sequence of
> POP %reg; ADD $x, %RSP; POP %reg forces emission of synchronization
> uop to synchronize the value of the stack pointer in the stack engine
> and the out-of-order core.
> 
> Using POP with the dummy register instead of ADD $x, %RSP results in a
> smaller code size and faster code.
> 
> The patch also fixes the reference to the wrong register in the
> nearby comment.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> ---

Pushed to branch `for_paolo/6.1` at:

    https://github.com/sean-jc/linux.git

Unless you hear otherwise, it will make its way to kvm/queue "soon".

Note, the commit IDs are not guaranteed to be stable.