linux-kernel - Re: [PATCH] x86/bugs/mmio: Rename mmio_stale_data_clear to cpu_buf_vm

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Message-ID: <Z_gsgHzgGWqnNwKv@google.com>
Date: Thu, 10 Apr 2025 13:39:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org, 
	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] x86/bugs/mmio: Rename mmio_stale_data_clear to cpu_buf_vm_clear

On Thu, Apr 10, 2025, Pawan Gupta wrote:
> The static key mmio_stale_data_clear controls the KVM-only mitigation for
> MMIO Stale Data vulnerability. Rename it to reflect its purpose.
> 
> No functional change.
> 
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> ---
>  arch/x86/include/asm/nospec-branch.h |  2 +-
>  arch/x86/kernel/cpu/bugs.c           | 16 ++++++++++------
>  arch/x86/kvm/vmx/vmx.c               |  2 +-
>  3 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index 8a5cc8e70439e10aab4eeb5b0f5e116cf635b43d..c0474e2b741737dad129159adf3b5fc056b6097c 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -561,7 +561,7 @@ DECLARE_STATIC_KEY_FALSE(mds_idle_clear);
>  
>  DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
>  
> -DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear);
> +DECLARE_STATIC_KEY_FALSE(cpu_buf_vm_clear);

Could we tack on "if_mmio" or something?  E.g. cpu_buf_vm_clear_if_mmio.  FWIW,
I don't love that name, so if anyone can come up with something better...

I like the idea of tying the static key back to X86_FEATURE_CLEAR_CPU_BUF, but
when looking at just the usage in KVM, "cpu_buf_vm_clear" doesn't provide any
hints as to when/why KVM needs to clear buffers.