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bh=KHefnsd9D4gYX0qAxPmeOq8/AUrqApnE1/2yVtKtDLA=; b=mGyOX15gaqYFCfyOT/KoNVJvr3jwb8Ljph6ESWwQEUaLgnuXQT+ZwURmcSlmyQc4Jq2C3a hHTFjHghjZENj/Ag== From: "tip-bot2 for Kim Phillips" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/sev] x86/speculation: Do not enable Automatic IBRS if SEV-SNP is enabled Cc: Kim Phillips , Michael Roth , "Borislav Petkov (AMD)" , Dave Hansen , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20240126041126.1927228-3-michael.roth@amd.com> References: <20240126041126.1927228-3-michael.roth@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <170663197187.398.15168561144334587796.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1789534807823339245 X-GMAIL-MSGID: 1789534807823339245 The following commit has been merged into the x86/sev branch of tip: Commit-ID: acaa4b5c4c854b5009f4d4a5395b2609ad0f4937 Gitweb: https://git.kernel.org/tip/acaa4b5c4c854b5009f4d4a5395b2609ad0f4937 Author: Kim Phillips AuthorDate: Thu, 25 Jan 2024 22:11:02 -06:00 Committer: Borislav Petkov (AMD) CommitterDate: Mon, 29 Jan 2024 17:19:01 +01:00 x86/speculation: Do not enable Automatic IBRS if SEV-SNP is enabled 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 and all back to retpolines instead. [ mdr: squash in changes from review discussion. ] Signed-off-by: Kim Phillips Signed-off-by: Michael Roth Signed-off-by: Borislav Petkov (AMD) Acked-by: Dave Hansen Link: https://lore.kernel.org/r/20240126041126.1927228-3-michael.roth@amd.com --- arch/x86/kernel/cpu/common.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 0b97bcd..9e35e27 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1355,8 +1355,13 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) /* * AMD's AutoIBRS is equivalent to Intel's eIBRS - use the Intel feature * flag and protect from vendor-specific bugs via the whitelist. + * + * Don't use AutoIBRS when SNP is enabled because it degrades host + * userspace indirect branch performance. */ - if ((ia32_cap & ARCH_CAP_IBRS_ALL) || cpu_has(c, X86_FEATURE_AUTOIBRS)) { + if ((ia32_cap & ARCH_CAP_IBRS_ALL) || + (cpu_has(c, X86_FEATURE_AUTOIBRS) && + !cpu_feature_enabled(X86_FEATURE_SEV_SNP))) { setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED); if (!cpu_matches(cpu_vuln_whitelist, NO_EIBRS_PBRSB) && !(ia32_cap & ARCH_CAP_PBRSB_NO))