From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1FB7D42A79B for ; Wed, 1 Jul 2026 19:33:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782934408; cv=none; b=KV6iN3jd1redPDhNVyApGSAlGVEEc5F2fcgoTM7moZDw6b3oaMG6w6Hn9F3vory8tSniSQW+FW4is/yWtHf6HWKHf5TM/v3sxMMjDlTQOcCBijNjzVhFhtnEJmG2EdAID1VdP+ujqcpaV9m8Qs8K/pDxIg/MzG7cH0AmHhTxnIY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782934408; c=relaxed/simple; bh=y0eTf6sBBqtgXOMcKj6+dRH4mQYHxDct/p+oWayuTuo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=BPl4jGo1y/ADTiStQ/M2HlFsEZRwg7zutyGY2h6AKPFS8lwJ8rdpsrqPSWomlRp2XLn9l+TSl89l1UeMQgTz9z9aETwERSEat79iDm9IkoUev1etTmteutHhG17MAU67mflLjQ0ixiRYesNFZESIvmmMtTDzKRRB7yWy/WLTtUo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ORv/wTaK; arc=none smtp.client-ip=209.85.214.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ORv/wTaK" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-2c9b1b608e2so14576825ad.3 for ; Wed, 01 Jul 2026 12:33:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1782934404; x=1783539204; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=KILxImADtcVlkoacCtqYmxEGcZEGxD9ytdtd9JfAHyU=; b=ORv/wTaKsBNfrlgPBKO36ChLCvIYqPwt+9YgP2EYpb107ecgI+M6x7F4Asrp14zCL6 P6NwaDasmbBajfykLu+Odi07szGE8BbYtW/T9BLAxfLqV29xo3tsqL3H0G8k/dovuaH7 kwYTeFNkhaYGlJPcbfzVtA0soBGDTYwtAvY+NrGl9Y1bNR2dz1e+jdRx0E4JYpNtlVuC qxqvTybx+4bfBuSCwtg48ZsRALQRFyVPNxYzgfGe5TnJ5bjbSPUdcIL4h1wpB9s7mHM0 9Ebb+z1kGb9uz+VSwmKTJfZZiAm/VBVf5G659v54ZKJwZOfiAVBLlY7vQjH8xxWQa8Rd zZ6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782934404; x=1783539204; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=KILxImADtcVlkoacCtqYmxEGcZEGxD9ytdtd9JfAHyU=; b=KtugGFVfp1e6TTzeO16QcDdK6J2uW9xM0l3XWY0btj25cfyWOSJthDrAUR3QbSP9pt d19JQffyRcJADnLmBJy6e4v8va2SscclGuoMyEPPdtGMrhz0arCqsh4uyWsU7t9F1uvA fTrtZu4whLs0Jd1M3oDc1O9OdaH8D58oqO2ZtSH1pNX+9HP1IzSM6vrKzAyOXTw0GE7B PoQByZAxWx7oDl6KmOrK4GkY4JjVJZSUaV27CKmovQHr4NZilQfytmsfPA0wswQMqoxA gevM0JNscC58kSMN4ZXiV2cj1wwJw0M9ib5lPArCJxFpGg4X53qX6zYNkCdVLth8jwXN kttw== X-Forwarded-Encrypted: i=1; AHgh+RqNwPw8q30u9OERVqcAW3DW6v2SESb9kqaowWGFFDDmTfBr/GPAsmfWgodsFDv7DCnVOQuzmJBMzrZi@lists.linux.dev X-Gm-Message-State: AOJu0Ywo5kbnR3CNdR0ueo8dm6VOI1h7pebSiSwWCZ1ypdJC+hdU7nDx IEZWKoJ5BDus4yhi/f7CKKzBXWQEiekwWCKejafwfIot0fCehd9B7leSlRkE+qBGs71ClnpVR/s vKK2CZg== X-Received: from pltf1.prod.google.com ([2002:a17:902:74c1:b0:2c7:5af7:37a3]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:c952:b0:2c9:c169:7483 with SMTP id d9443c01a7336-2ca7e87dc6bmr34187285ad.37.1782934403691; Wed, 01 Jul 2026 12:33:23 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 1 Jul 2026 12:32:08 -0700 In-Reply-To: <20260701193212.749551-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260701193212.749551-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.rc0.799.gd6f94ed593-goog Message-ID: <20260701193212.749551-48-seanjc@google.com> Subject: [PATCH v5 47/51] x86/paravirt: Don't use a PV sched_clock in CoCo guests with trusted TSC From: Sean Christopherson To: Jonathan Corbet , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Rick Edgecombe , Sean Christopherson , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , John Stultz Cc: Shuah Khan , "H. Peter Anvin" , Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, xen-devel@lists.xenproject.org, Tom Lendacky , Nikunj A Dadhania , David Woodhouse , David Woodhouse , Michael Kelley , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Silently ignore attempts to switch to a paravirt sched_clock when running as a CoCo guest with trusted TSC. In hand-wavy theory, a misbehaving hypervisor could attack the guest by manipulating the PV clock to affect guest scheduling in some weird and/or predictable way. More importantly, reading TSC on such platforms is faster than any PV clock, and sched_clock is all about speed. Reviewed-by: David Woodhouse Signed-off-by: Sean Christopherson --- arch/x86/kernel/tsc.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 012321fed5e5..a146fc7b5e74 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -283,6 +283,15 @@ bool using_native_sched_clock(void) int __init __paravirt_set_sched_clock(u64 (*func)(void), bool stable, void (*save)(void), void (*restore)(void)) { + /* + * Don't replace TSC with a PV clock when running as a CoCo guest and + * the TSC is secure/trusted; PV clocks are emulated by the hypervisor, + * which isn't in the guest's TCB. + */ + if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC) || + boot_cpu_has(X86_FEATURE_TDX_GUEST)) + return -EPERM; + if (!stable) clear_sched_clock_stable(); -- 2.55.0.rc0.799.gd6f94ed593-goog