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Wed, 25 Oct 2023 17:33:36 +0000 (UTC) Date: Wed, 25 Oct 2023 19:33:31 +0200 From: Borislav Petkov To: Michael Roth Cc: kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com, zhi.a.wang@intel.com, Kim Phillips Subject: Re: [PATCH v10 05/50] x86/speculation: Do not enable Automatic IBRS if SEV SNP is enabled Message-ID: <20231025173331.GCZTlRa3Tzfc1fHvCu@fat_crate.local> References: <20231016132819.1002933-1-michael.roth@amd.com> <20231016132819.1002933-6-michael.roth@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20231016132819.1002933-6-michael.roth@amd.com> X-Rspamd-Queue-Id: 76A2A4001B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: w9eorgsj3hirnexwark4ef1eb8m7rhij X-HE-Tag: 1698255263-207072 X-HE-Meta: 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 7/So7P6g +Mvqx+l6GeSH1bOphEsqctY96R+8PA0cHPRX0jTtBTRbQMF2zmvwgcrfDG4buo7Lz3yGRgN3k10LBeJNqNrOneXBA+vwwGpx7I00yrUAZZd0i6iOiCiluuhxo+8CoZMzRL8dD+r7E8NP/eAbaJavWa16z4P3wDXzIYDWYDVEOOFaCfhKpnKqo+9AOlssDbRdUCCO0EcvHMQXdoI9y1XPkaKuMJo6r698vL/ls X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 16, 2023 at 08:27:34AM -0500, Michael Roth wrote: > From: Kim Phillips > > Without SEV-SNP, Automatic IBRS protects only the kernel. But when > SEV-SNP is enabled, the Automatic IBRS protection umbrella widens to all > host-side code, including userspace. This protection comes at a cost: > reduced userspace indirect branch performance. > > To avoid this performance loss, don't use Automatic IBRS on SEV-SNP > hosts. Fall back to retpolines instead. > > Signed-off-by: Kim Phillips > [mdr: squash in changes from review discussion] > Signed-off-by: Michael Roth > --- > arch/x86/kernel/cpu/common.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) Acked-by: Borislav Petkov (AMD) -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette