linux-kernel - Re: [PATCH 0/4] KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling

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Message-ID: <176254658743.821204.2042588290407024138.b4-ty@google.com>
Date: Mon, 10 Nov 2025 07:37:19 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jon Kohler <jon@...anix.com>
Subject: Re: [PATCH 0/4] KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling

On Thu, 30 Oct 2025 15:42:42 -0700, Sean Christopherson wrote:
> This series is the result of the recent PUCK discussion[*] on optimizing the
> XCR0/XSS loads that are currently done on every VM-Enter and VM-Exit.  My
> initial thought that swapping XCR0/XSS outside of the fastpath was spot on;
> turns out the only reason they're swapped in the fastpath is because of a
> hack-a-fix that papered over an egregious #MC handling bug where the kernel #MC
> handler would call schedule() from an atomic context.  The resulting #GP due to
> trying to swap FPU state with a guest XCR0/XSS was "fixed" by loading the host
> values before handling #MCs from the guest.
> 
> [...]

Applied to kvm-x86 misc, thanks!

[1/4] KVM: SVM: Handle #MCs in guest outside of fastpath
      https://github.com/kvm-x86/linux/commit/6e640bb5caab
[2/4] KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath
      https://github.com/kvm-x86/linux/commit/8934c592bcbf
[3/4] KVM: x86: Load guest/host XCR0 and XSS outside of the fastpath run loop
      https://github.com/kvm-x86/linux/commit/3377a9233d30
[4/4] KVM: x86: Load guest/host PKRU outside of the fastpath run loop
      https://github.com/kvm-x86/linux/commit/7df3021b622f

--
https://github.com/kvm-x86/linux/tree/next