linux-kernel - Re: [PATCH v7 0/3] KVM: SVM: Flush cache only on CPUs running SEV guest

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Message-ID: <Z75wYblH3_IFsoUW@google.com>
Date: Tue, 25 Feb 2025 17:37:37 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Zheyun Shen <szy0127@...u.edu.cn>
Cc: thomas.lendacky@....com, pbonzini@...hat.com, tglx@...utronix.de, 
	kevinloughlin@...gle.com, mingo@...hat.com, bp@...en8.de, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 0/3] KVM: SVM: Flush cache only on CPUs running SEV guest

On Tue, Jan 28, 2025, Zheyun Shen wrote:
> Previous versions pointed out the problem of wbinvd_on_all_cpus() in SEV
> and tried to maintain a cpumask to solve it. This version includes
> further code cleanup.
> 
> Although dirty_mask is not maintained perfectly and may lead to wbinvd on 
> physical CPUs that are not running a SEV guest, it's still better than 
> wbinvd_on_all_cpus(). And vcpu migration is designed to be solved in 
> future work.

I have a variety of comments, but no need to send a new version.  I'm going to
post a combined version with the WBNOINVD series, hopefully tomorrow.

The only thing that needs your attention is the pre_sev_run() => sev_vcpu_load()
change between v3 and v4.

> ---
> v6 -> v7:
> - Fixed the writing oversight in sev_vcpu_load().
> 
> v5 -> v6:
> - Replaced sev_get_wbinvd_dirty_mask() with the helper function 
> to_kvm_sev_info().
> 
> v4 -> v5:
> - rebase to tip @ 15e2f65f2ecf .
> - Added a commit to remove unnecessary calls to wbinvd().
> - Changed some comments.
> 
> v3 -> v4:
> - Added a wbinvd helper and export it to SEV.
> - Changed the struct cpumask in kvm_sev_info into cpumask*, which should
> be dynamically allocated and freed.
> - Changed the time of recording the CPUs from pre_sev_run() to vcpu_load().
> - Removed code of clearing the mask.
> 
> v2 -> v3:
> - Replaced get_cpu() with parameter cpu in pre_sev_run().
> 
> v1 -> v2:
> - Added sev_do_wbinvd() to wrap two operations.
> - Used cpumask_test_and_clear_cpu() to avoid concurrent problems.
> ---
> 
> Zheyun Shen (3):
>   KVM: x86: Add a wbinvd helper
>   KVM: SVM: Remove wbinvd in sev_vm_destroy()
>   KVM: SVM: Flush cache only on CPUs running SEV guest
> 
>  arch/x86/kvm/svm/sev.c | 36 +++++++++++++++++++++++++++---------
>  arch/x86/kvm/svm/svm.c |  2 ++
>  arch/x86/kvm/svm/svm.h |  5 ++++-
>  arch/x86/kvm/x86.c     |  9 +++++++--
>  arch/x86/kvm/x86.h     |  1 +
>  5 files changed, 41 insertions(+), 12 deletions(-)
> 
> -- 
> 2.34.1
>