From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Andrew Cooper <Andrew.Cooper3@citrix.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Hans de Goede <hdegoede@redhat.com>,
"Rafael J . Wysocki" <rafael@kernel.org>,
Pavel Machek <pavel@ucw.cz>, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH] x86/cpu: Avoid writing MSR_IA32_TSX_CTRL when writing it is not supported
Date: Wed, 7 Sep 2022 18:03:29 -0700 [thread overview]
Message-ID: <20220908010329.rhetlp6plqlaiegf@desk> (raw)
In-Reply-To: <c076b593-815b-f7b2-4eab-9d2087580a71@citrix.com>
On Tue, Sep 06, 2022 at 11:00:08PM +0000, Andrew Cooper wrote:
> On 06/09/2022 22:00, Peter Zijlstra wrote:
> > On Tue, Sep 06, 2022 at 10:56:47PM +0200, Hans de Goede wrote:
> >> Hi,
> >>
> >> On 9/6/22 22:43, Peter Zijlstra wrote:
> >>> On Tue, Sep 06, 2022 at 10:17:43PM +0200, Hans de Goede wrote:
> >>>> On an Intel Atom N2600 (and presumable other Cedar Trail models)
> >>>> MSR_IA32_TSX_CTRL can be read, causing saved_msr.valid to be set for it
> >>>> by msr_build_context().
> >>>>
> >>>> This causes restore_processor_state() to try and restore it, but writing
> >>>> this MSR is not allowed on the Intel Atom N2600 leading to:
> >>> FWIW, virt tends to do this same thing a lot. They'll allow reading
> >>> random MSRs and only fail on write.
> >> Right. So I guess I should send a v2 with an updated commit
> >> message mentioning this ?
> > Nah, just saying this is a somewhat common pattern with MSRs.
> >
> > The best ones are the one where writing the value read is invalid :/ or
> > those who also silently eat a 0 write just for giggles. Luckily that
> > doesn't happen often.
>
> Several comments. First of all, MSR_TSX_CTRL is a fully read/write
> MSR. If virt is doing this wrong, fix the hypervisor. But this doesn't
> look virt related?
>
> More importantly, MSR_TSX_CTRL does not plausibly exist on an Atom
> N2600, as it is more than a decade old.
>
> MSR_TSX_CTRL was retrofitted in microcode to the MDS_NO, TAA-vulnerable
> CPUs which is a very narrow range from about 1 quarter of 2019 which
> includes Cascade Lake, and then included architecturally on subsequent
> parts which support TSX.
>
> pm_save_spec_msr() is totally broken. It's poking MSRs blindly without
> checking the enumeration of the capability first.
pm_save_spec_msr() relies on valid-msr-check in build_msr_context(), but
obviously it is not working in this particular case.
Does adding the enumeration check as below looks okay:
(I am not sure if I got the enumeration right for MSR_AMD64_LS_CFG).
---
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 8cbf623f0ecf..a750c1a1964b 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -76,6 +76,8 @@ static inline void init_ia32_feat_ctl(struct cpuinfo_x86 *c) {}
extern __noendbr void cet_disable(void);
+extern bool spec_msr_valid(u32 msr_id);
+
struct ucode_cpu_info;
int intel_cpu_collect_info(struct ucode_cpu_info *uci);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3e508f239098..7430a36fd7ae 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1278,6 +1278,26 @@ static bool __init cpu_matches(const struct x86_cpu_id *table, unsigned long whi
return m && !!(m->driver_data & which);
}
+bool spec_msr_valid(u32 msr_id)
+{
+ u64 ia32_cap = x86_read_arch_cap_msr();
+
+ switch (msr_id) {
+ case MSR_IA32_SPEC_CTRL:
+ return boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL);
+ case MSR_IA32_TSX_CTRL:
+ return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
+ case MSR_TSX_FORCE_ABORT:
+ return boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT);
+ case MSR_IA32_MCU_OPT_CTRL:
+ return boot_cpu_has(X86_FEATURE_SRBDS_CTRL);
+ case MSR_AMD64_LS_CFG:
+ return boot_cpu_has(X86_FEATURE_LS_CFG_SSBD);
+ }
+
+ return false;
+}
+
u64 x86_read_arch_cap_msr(void)
{
u64 ia32_cap = 0;
diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index bb176c72891c..8db73f7982c7 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -520,8 +520,12 @@ static void pm_save_spec_msr(void)
MSR_IA32_MCU_OPT_CTRL,
MSR_AMD64_LS_CFG,
};
+ int i;
- msr_build_context(spec_msr_id, ARRAY_SIZE(spec_msr_id));
+ for (i=0; i < ARRAY_SIZE(spec_msr_id); i++) {
+ if (spec_msr_valid(spec_msr_id[i]))
+ msr_build_context(&spec_msr_id[i], 1);
+ }
}
static int pm_check_save_msr(void)
next prev parent reply other threads:[~2022-09-08 1:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-06 20:17 [PATCH] x86/cpu: Avoid writing MSR_IA32_TSX_CTRL when writing it is not supported Hans de Goede
2022-09-06 20:43 ` Peter Zijlstra
2022-09-06 20:56 ` Hans de Goede
2022-09-06 21:00 ` Peter Zijlstra
2022-09-06 23:00 ` Andrew Cooper
2022-09-07 7:32 ` Hans de Goede
2022-09-08 13:34 ` Andrew Cooper
2022-09-08 1:03 ` Pawan Gupta [this message]
2022-09-08 13:46 ` Andrew Cooper
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