linux-kernel - Re: [PATCH v2 0/4] KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling

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Message-ID: <176375129628.290245.2248166569099413567.b4-ty@google.com>
Date: Fri, 21 Nov 2025 10:55:31 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	"Kirill A. Shutemov" <kas@...nel.org>
Cc: kvm@...r.kernel.org, x86@...nel.org, linux-coco@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Jon Kohler <jon@...anix.com>, Tony Lindgren <tony.lindgren@...ux.intel.com>
Subject: Re: [PATCH v2 0/4] KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling

On Tue, 18 Nov 2025 14:23:24 -0800, Sean Christopherson wrote:
> Optimize XCR0/XSS loads that are currently done on every VM-Enter and VM-Exit,
> by handling them outside of KVM's fastpath inner loop.
> 
> Context switching at entry/exit is unnecessary behavior inherited from a
> hack-a-fix that papered over an egregious #MC handling bug where the kernel #MC
> handler would call schedule() from atomic contexts.  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/ebd1a3365500
[2/4] KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath
      https://github.com/kvm-x86/linux/commit/63669bd1d50f
[3/4] KVM: x86: Load guest/host XCR0 and XSS outside of the fastpath run loop
      https://github.com/kvm-x86/linux/commit/75c69c82f211
[4/4] KVM: x86: Load guest/host PKRU outside of the fastpath run loop
      https://github.com/kvm-x86/linux/commit/7649412af3ea

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