linux-kernel - Re: [PATCH] KVM/VMX: Do not declare vmread

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Message-ID: <Yxolh+QhLocER0oY@google.com>
Date:   Thu, 8 Sep 2022 17:25:27 +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: Do not declare vmread_error asmlinkage

On Wed, Aug 17, 2022, Uros Bizjak wrote:
> There is no need to declare vmread_error asmlinkage, its arguments
> can be passed via registers for both, 32-bit and 64-bit targets.
> Function argument registers are considered call-clobbered registers,
> they are saved in the trampoline just before the function call and
> restored afterwards.
> 
> Note that asmlinkage and __attribute__((regparm(0))) have no effect
> on 64-bit targets. The trampoline is called from the assembler glue
> code that implements its own stack-passing function calling convention,
> so the attribute on the trampoline declaration does not change anything
> for 64-bit as well as 32-bit targets. We can declare it asmlinkage for
> documentation purposes.
> 
> The patch unifies trampoline function argument handling between 32-bit
> and 64-bit targets and improves generated code for 32-bit targets.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> ---

Minus the vmread_error_trampoline() change, 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.