From: "Nikunj A. Dadhania" <nikunj@amd.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: <kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] KVM: SVM: Refresh vcpu->arch.cr{0,3} prior to invoking fastpath handler
Date: Fri, 24 Apr 2026 14:15:47 +0530 [thread overview]
Message-ID: <7f27de9d-de4d-4aa2-9ce9-35b49990c894@amd.com> (raw)
In-Reply-To: <20260423162628.490962-3-seanjc@google.com>
On 4/23/2026 9:56 PM, Sean Christopherson wrote:
> Refresh KVM's copies of CR0 and CR3 from the VMCB prior to (potentially)
> invoking a fastpath handler to ensure that KVM doesn't consume stale
> state. While it's unlikely KVM will ever consume CR3 or CR0.{TS,MP} in
> the fastpath, grabbing the values from the VMCB is inexpensive, i.e. the
> risk of subtle bugs far outweighs the reward of deferring reads for a
> small subset of VM-Exits.
This also keeps CR0/CR3 current during the fast-reenter loop in
vcpu_enter_guest(), which previously skipped svm_handle_exit() entirely.
>
> Note, KVM doesn't currently consume CR3 or CR0.{TS,MP} in the fastpath,
> as KVM requires next_rip to be valid (i.e. KVM doesn't read CR3 to decode
> the instruction), CR0.MP is never consumed, and CR0.TS is only consumed by
> the full emulator.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Nikunj A. Dadhania <nikunj@amd.com>
prev parent reply other threads:[~2026-04-24 8:45 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-23 16:26 [PATCH 0/2] KVM: x86: Fastpath userspace exit fix and hardening Sean Christopherson
2026-04-23 16:26 ` [PATCH 1/2] KVM: x86: Ensure vendor's exit handler runs before fastpath userspace exits Sean Christopherson
2026-04-23 21:48 ` Huang, Kai
2026-04-24 4:29 ` Nikunj A. Dadhania
2026-04-23 16:26 ` [PATCH 2/2] KVM: SVM: Refresh vcpu->arch.cr{0,3} prior to invoking fastpath handler Sean Christopherson
2026-04-24 8:45 ` Nikunj A. Dadhania [this message]
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