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Thu, 14 Aug 2025 12:03:59 -0700 (PDT) Date: Thu, 14 Aug 2025 12:03:57 -0700 In-Reply-To: <20250813183728.2070321-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <2025081209-porcupine-shut-1d95@gregkh> <20250813183728.2070321-1-sashal@kernel.org> Message-ID: Subject: Re: [PATCH 6.6.y] KVM: VMX: Allow guest to set DEBUGCTL.RTM_DEBUG if RTM is supported From: Sean Christopherson To: Sasha Levin Cc: stable@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Wed, Aug 13, 2025, Sasha Levin wrote: > From: Sean Christopherson > > [ Upstream commit 17ec2f965344ee3fd6620bef7ef68792f4ac3af0 ] > > Let the guest set DEBUGCTL.RTM_DEBUG if RTM is supported according to the > guest CPUID model, as debug support is supposed to be available if RTM is > supported, and there are no known downsides to letting the guest debug RTM > aborts. > > Note, there are no known bug reports related to RTM_DEBUG, the primary > motivation is to reduce the probability of breaking existing guests when a > future change adds a missing consistency check on vmcs12.GUEST_DEBUGCTL > (KVM currently lets L2 run with whatever hardware supports; whoops). > > Note #2, KVM already emulates DR6.RTM, and doesn't restrict access to > DR7.RTM. > > Fixes: 83c529151ab0 ("KVM: x86: expose Intel cpu new features (HLE, RTM) to guest") > Cc: stable@vger.kernel.org > Link: https://lore.kernel.org/r/20250610232010.162191-5-seanjc@google.com > Signed-off-by: Sean Christopherson > [ Changed guest_cpu_cap_has to guest_cpuid_has ] > Signed-off-by: Sasha Levin > --- Acked-by: Sean Christopherson