From: Tony Lindgren <tony.lindgren@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
"Kirill A. Shutemov" <kas@kernel.org>,
kvm@vger.kernel.org, x86@kernel.org, linux-coco@lists.linux.dev,
linux-kernel@vger.kernel.org,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Jon Kohler <jon@nutanix.com>
Subject: Re: [PATCH v2 2/4] KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath
Date: Wed, 19 Nov 2025 08:11:38 +0200 [thread overview]
Message-ID: <aR1fmtagimoLw_5U@tlindgre-MOBL1> (raw)
In-Reply-To: <20251118222328.2265758-3-seanjc@google.com>
On Tue, Nov 18, 2025 at 02:23:26PM -0800, Sean Christopherson wrote:
> Handle Machine Checks (#MC) that happen on VM-Enter (VMX or TDX) outside
> of KVM's fastpath so that as much host state as possible is re-loaded
> before invoking the kernel's #MC handler. The only requirement is that
> KVM invokes the #MC handler before enabling IRQs (and even that could
> _probably_ be related to handling #MCs before enabling preemption).
>
> Waiting to handle #MCs until "more" host state is loaded hardens KVM
> against flaws in the #MC handler, which has historically been quite
> brittle. E.g. prior to commit 5567d11c21a1 ("x86/mce: Send #MC singal from
> task work"), the #MC code could trigger a schedule() with IRQs and
> preemption disabled. That led to a KVM hack-a-fix in commit 1811d979c716
> ("x86/kvm: move kvm_load/put_guest_xcr0 into atomic context").
>
> Note, vmx_handle_exit_irqoff() is common to VMX and TDX guests.
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
next prev parent reply other threads:[~2025-11-19 6:11 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-18 22:23 [PATCH v2 0/4] KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling Sean Christopherson
2025-11-18 22:23 ` [PATCH v2 1/4] KVM: SVM: Handle #MCs in guest outside of fastpath Sean Christopherson
2025-11-18 22:23 ` [PATCH v2 2/4] KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath Sean Christopherson
2025-11-19 6:11 ` Tony Lindgren [this message]
2025-11-21 6:09 ` Binbin Wu
2025-11-21 18:58 ` Sean Christopherson
2025-11-18 22:23 ` [PATCH v2 3/4] KVM: x86: Load guest/host XCR0 and XSS outside of the fastpath run loop Sean Christopherson
2025-11-18 22:23 ` [PATCH v2 4/4] KVM: x86: Load guest/host PKRU " Sean Christopherson
2025-11-21 18:55 ` [PATCH v2 0/4] KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling Sean Christopherson
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