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AJvYcCWwTlok7DvMEFNHBLjQAppaKQxaQpTUx7dRwA2fqWEqxG2D6HQi/muOstZkQ+xk7+y+hpURYdQhSEE=@vger.kernel.org X-Gm-Message-State: AOJu0YyQ6GmpTGWIwI/CNp0NQpEqwuO2KtufsZkOPXNyxOYd5JCwXPjX 1PSdI5iApUgHSHnnTZ7NVKSaCQfG138bKxufxFg+3sO9oAxQ1WDW9xM9EhnWSdev45cu1ZFYPTq okw== X-Google-Smtp-Source: AGHT+IF7FvBz2XtjdY1Gwm2snh7AYTh3FwqQtsFxghocXrvK4VvzfqD2ppJPcFtt7H5IcBLLk5+tAerZoio= X-Received: from plrs9.prod.google.com ([2002:a17:902:b189:b0:223:5416:c809]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:f543:b0:224:2a6d:55ae with SMTP id d9443c01a7336-22e1eac1872mr163309125ad.48.1746484638786; Mon, 05 May 2025 15:37:18 -0700 (PDT) Date: Mon, 5 May 2025 15:37:17 -0700 In-Reply-To: <20250505221419.2672473-317-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250505221419.2672473-1-sashal@kernel.org> <20250505221419.2672473-317-sashal@kernel.org> Message-ID: Subject: Re: [PATCH AUTOSEL 6.14 317/642] x86/bugs: KVM: Add support for SRSO_MSR_FIX From: Sean Christopherson To: Sasha Levin Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Borislav Petkov , tglx@linutronix.de, peterz@infradead.org, jpoimboe@kernel.org, corbet@lwn.net, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, pbonzini@redhat.com, thomas.lendacky@amd.com, mario.limonciello@amd.com, perry.yuan@amd.com, kai.huang@intel.com, xiaoyao.li@intel.com, tony.luck@intel.com, xin3.li@intel.com, kan.liang@linux.intel.com, linux-doc@vger.kernel.org, kvm@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Mon, May 05, 2025, Sasha Levin wrote: > From: Borislav Petkov > > [ Upstream commit 8442df2b49ed9bcd67833ad4f091d15ac91efd00 ] > > Add support for > > CPUID Fn8000_0021_EAX[31] (SRSO_MSR_FIX). If this bit is 1, it > indicates that software may use MSR BP_CFG[BpSpecReduce] to mitigate > SRSO. > > Enable BpSpecReduce to mitigate SRSO across guest/host boundaries. > > Switch back to enabling the bit when virtualization is enabled and to > clear the bit when virtualization is disabled because using a MSR slot > would clear the bit when the guest is exited and any training the guest > has done, would potentially influence the host kernel when execution > enters the kernel and hasn't VMRUN the guest yet. > > More detail on the public thread in Link below. > > Co-developed-by: Sean Christopherson > Signed-off-by: Sean Christopherson > Signed-off-by: Borislav Petkov (AMD) > Link: https://lore.kernel.org/r/20241202120416.6054-1-bp@kernel.org > Signed-off-by: Sasha Levin > --- Can we please hold off on this until the fix lands[1]? This version introduces a very measurable performance regression[2] for non-KVM use cases. [1] https://lore.kernel.org/all/20250502223456.887618-1-seanjc@google.com [2] https://www.phoronix.com/review/linux-615-amd-regression