linux-kernel - Re: [PATCH v2 8/8] KVM: SVM: Flush cache only on CPUs running SEV guest

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Message-ID: <8a16978a-2f02-a9bb-05b0-368e3ee8e284@amd.com>
Date: Mon, 19 May 2025 12:48:55 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, Zheyun Shen <szy0127@...u.edu.cn>,
 Kevin Loughlin <kevinloughlin@...gle.com>, Kai Huang <kai.huang@...el.com>,
 Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH v2 8/8] KVM: SVM: Flush cache only on CPUs running SEV
 guest

On 5/16/25 16:28, Sean Christopherson wrote:
> From: Zheyun Shen <szy0127@...u.edu.cn>
> 
> On AMD CPUs without ensuring cache consistency, each memory page
> reclamation in an SEV guest triggers a call to do WBNOINVD/WBINVD on all
> CPUs, thereby affecting the performance of other programs on the host.
> 
> Typically, an AMD server may have 128 cores or more, while the SEV guest
> might only utilize 8 of these cores. Meanwhile, host can use qemu-affinity
> to bind these 8 vCPUs to specific physical CPUs.
> 
> Therefore, keeping a record of the physical core numbers each time a vCPU
> runs can help avoid flushing the cache for all CPUs every time.
> 
> Signed-off-by: Zheyun Shen <szy0127@...u.edu.cn>
> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  arch/x86/kvm/svm/sev.c | 46 +++++++++++++++++++++++++++++++++++-------
>  arch/x86/kvm/svm/svm.h |  1 +
>  2 files changed, 40 insertions(+), 7 deletions(-)
>