From: Bagas Sanjaya <bagasdotme@gmail.com>
To: Yosry Ahmed <yosry.ahmed@linux.dev>,
Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jim Mattson <jmattson@google.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: x86: Document a virtualization gap for GIF on AMD CPUs
Date: Fri, 31 Oct 2025 07:09:38 +0700 [thread overview]
Message-ID: <aQP-Qv1SOi0cy-nO@archie.me> (raw)
In-Reply-To: <20251030223757.2950309-1-yosry.ahmed@linux.dev>
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On Thu, Oct 30, 2025 at 10:37:57PM +0000, Yosry Ahmed wrote:
> -TBD
> +On AMD CPUs, when GIF is cleared, #DB exceptions or traps due to a breakpoint
> +register match are ignored and discarded by the CPU. The CPU relies on the VMM
> +to fully virtualize this behavior, even when vGIF is enabled for the guest
> +(i.e. vGIF=0 does not cause the CPU to drop #DBs when the guest is running).
> +KVM does not virtualize this behavior as the complexity is unjustified given
> +the rarity of the use case. One way to handle this would be for KVM to
> +intercept the #DB, temporarily disable the breakpoint, single-step over the
> +instruction, then re-enable the breakpoint.
The wording LGTM, thanks!
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
--
An old man doll... just what I always wanted! - Clara
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next prev parent reply other threads:[~2025-10-31 0:09 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-30 22:37 Yosry Ahmed
2025-10-31 0:09 ` Bagas Sanjaya [this message]
2025-11-18 23:27 ` Sean Christopherson
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