From: Sean Christopherson <seanjc@google.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, Reiji Watanabe <reijiw@google.com>,
Jim Mattson <jmattson@google.com>,
Andy Lutomirski <luto@kernel.org>,
Sean Christopherson <seanjc@google.com>
Subject: [PATCH 1/2] x86/cpu: Initialize MSR_TSC_AUX if RDTSCP *or* RDPID is supported
Date: Tue, 4 May 2021 15:56:31 -0700 [thread overview]
Message-ID: <20210504225632.1532621-2-seanjc@google.com> (raw)
In-Reply-To: <20210504225632.1532621-1-seanjc@google.com>
Initialize MSR_TSC_AUX with CPU node information if RDTSCP or RDPID is
supported. This fixes a bug where vdso_read_cpunode() will read garbage
via RDPID if RDPID is supported but RDTSCP is not. While no known CPU
supports RDPID but not RDTSCP, both Intel's SDM and AMD's APM allow for
RDPID to exist without RDTSCP, e.g. it's technically a legal CPU model
for a virtual machine.
Note, technically MSR_TSC_AUX could be initialized if and only if RDPID
is supported since RDTSCP is currently not used to retrieve the CPU node.
But, the cost of the superfluous WRMSR is negigible, whereas leaving
MSR_TSC_AUX uninitialized is just asking for future breakage if someone
decides to utilize RDTSCP.
Fixes: a582c540ac1b ("x86/vdso: Use RDPID in preference to LSL when available")
Cc: stable@vger.kernel.org
Cc: Reiji Watanabe <reijiw@google.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kernel/cpu/common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index ab640abe26b6..1e576cc831c1 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1850,7 +1850,7 @@ static inline void setup_getcpu(int cpu)
unsigned long cpudata = vdso_encode_cpunode(cpu, early_cpu_to_node(cpu));
struct desc_struct d = { };
- if (boot_cpu_has(X86_FEATURE_RDTSCP))
+ if (boot_cpu_has(X86_FEATURE_RDTSCP) || boot_cpu_has(X86_FEATURE_RDPID))
write_rdtscp_aux(cpudata);
/* Store CPU and node number in limit. */
--
2.31.1.527.g47e6f16901-goog
next prev parent reply other threads:[~2021-05-04 22:56 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-04 22:56 [PATCH 0/2] x86/cpu: RDPID+MSR_TSC_AUX fix and a cleanup Sean Christopherson
2021-05-04 22:56 ` Sean Christopherson [this message]
2021-05-06 12:14 ` [tip: x86/urgent] x86/cpu: Initialize MSR_TSC_AUX if RDTSCP *or* RDPID is supported tip-bot2 for Sean Christopherson
2021-05-04 22:56 ` [PATCH 2/2] x86/cpu: Remove write_tsc() and write_rdtscp_aux() wrappers Sean Christopherson
2021-05-06 12:14 ` [tip: x86/urgent] " tip-bot2 for Sean Christopherson
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