From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: KVM list <kvm@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
X86 ML <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
xen-devel <Xen-devel@lists.xen.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops
Date: Mon, 14 Mar 2016 13:02:03 +0100 [thread overview]
Message-ID: <20160314120202.GD15800__13694.7861676619$1457957040$gmane$org@pd.tnic> (raw)
In-Reply-To: <a3b871a4eb533340d04255409dfecc94f88c647d.1457805972.git.luto@kernel.org>
On Sat, Mar 12, 2016 at 10:08:49AM -0800, Andy Lutomirski wrote:
> This demotes an OOPS and likely panic due to a failed non-"safe" MSR
> access to a WARN_ONCE and, for RDMSR, a return value of zero. If
> panic_on_oops is set, then failed unsafe MSR accesses will still
> oops and panic.
>
> To be clear, this type of failure should *not* happen. This patch
> exists to minimize the chance of nasty undebuggable failures due on
> systems that used to work due to a now-fixed CONFIG_PARAVIRT=y bug.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/include/asm/msr.h | 10 ++++++++--
> arch/x86/mm/extable.c | 33 +++++++++++++++++++++++++++++++++
> 2 files changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
> index 93fb7c1cffda..1487054a1a70 100644
> --- a/arch/x86/include/asm/msr.h
> +++ b/arch/x86/include/asm/msr.h
> @@ -92,7 +92,10 @@ static inline unsigned long long native_read_msr(unsigned int msr)
> {
> DECLARE_ARGS(val, low, high);
>
> - asm volatile("rdmsr" : EAX_EDX_RET(val, low, high) : "c" (msr));
> + asm volatile("1: rdmsr\n"
> + "2:\n"
> + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_rdmsr_unsafe)
> + : EAX_EDX_RET(val, low, high) : "c" (msr));
> if (msr_tracepoint_active(__tracepoint_read_msr))
> do_trace_read_msr(msr, EAX_EDX_VAL(val, low, high), 0);
> return EAX_EDX_VAL(val, low, high);
> @@ -119,7 +122,10 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
> static inline void native_write_msr(unsigned int msr,
> unsigned low, unsigned high)
> {
> - asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high) : "memory");
> + asm volatile("1: wrmsr\n"
> + "2:\n"
> + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe)
This might be a good idea:
[ 0.220066] cpuidle: using governor menu
[ 0.224000] ------------[ cut here ]------------
[ 0.224000] WARNING: CPU: 0 PID: 1 at arch/x86/mm/extable.c:74 ex_handler_wrmsr_unsafe+0x73/0x80()
[ 0.224000] unchecked MSR access error: WRMSR to 0xdeadbeef (tried to write 0x000000000000caca)
[ 0.224000] Modules linked in:
[ 0.224000] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.5.0-rc7+ #7
[ 0.224000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[ 0.224000] 0000000000000000 ffff88007c0d7c08 ffffffff812f13a3 ffff88007c0d7c50
[ 0.224000] ffffffff81a40ffe ffff88007c0d7c40 ffffffff8105c3b1 ffffffff81717710
[ 0.224000] ffff88007c0d7d18 0000000000000000 ffffffff816207d0 0000000000000000
[ 0.224000] Call Trace:
[ 0.224000] [<ffffffff812f13a3>] dump_stack+0x67/0x94
[ 0.224000] [<ffffffff8105c3b1>] warn_slowpath_common+0x91/0xd0
[ 0.224000] [<ffffffff816207d0>] ? amd_cpu_notify+0x40/0x40
[ 0.224000] [<ffffffff8105c43c>] warn_slowpath_fmt+0x4c/0x50
[ 0.224000] [<ffffffff816207d0>] ? amd_cpu_notify+0x40/0x40
[ 0.224000] [<ffffffff8131de53>] ? __this_cpu_preempt_check+0x13/0x20
[ 0.224000] [<ffffffff8104efe3>] ex_handler_wrmsr_unsafe+0x73/0x80
and it looks helpful and all but when you do it pretty early - for
example I added a
wrmsrl(0xdeadbeef, 0xcafe);
at the end of pat_bsp_init() and the machine explodes with an early
panic. I'm wondering what is better - early panic or an early #GP from a
missing MSR.
And more specifically, can we do better to handle the early case
gracefully too?
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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next prev parent reply other threads:[~2016-03-14 12:02 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1457805972.git.luto@kernel.org>
2016-03-12 18:08 ` [PATCH v4 1/5] x86/paravirt: Add _safe to the read_msr and write_msr PV hooks Andy Lutomirski
2016-03-12 18:08 ` [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski
2016-03-12 18:08 ` [PATCH v4 3/5] x86/paravirt: Add paravirt_{read, write}_msr Andy Lutomirski
2016-03-12 18:08 ` [PATCH v4 4/5] x86/paravirt: Make "unsafe" MSR accesses unsafe even if PARAVIRT=y Andy Lutomirski
2016-03-12 18:08 ` [PATCH v4 5/5] x86/msr: Set the return value to zero when native_rdmsr_safe fails Andy Lutomirski
[not found] ` <7e72cd6ce08b946872a462fad13eca1810b8671d.1457805972.git.luto@kernel.org>
2016-03-14 11:57 ` [PATCH v4 1/5] x86/paravirt: Add _safe to the read_msr and write_msr PV hooks Borislav Petkov
[not found] ` <20160314115729.GC15800@pd.tnic>
2016-03-14 17:07 ` Andy Lutomirski
[not found] ` <a3b871a4eb533340d04255409dfecc94f88c647d.1457805972.git.luto@kernel.org>
2016-03-14 12:02 ` Borislav Petkov [this message]
[not found] ` <20160314120202.GD15800@pd.tnic>
2016-03-14 17:05 ` [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski
[not found] ` <CALCETrW6E0Nz6gSmRKTvHbQDhnHVpuhzmgZB1nZ3m-DL-Bt=tQ@mail.gmail.com>
2016-03-14 17:11 ` Linus Torvalds
2016-03-14 17:17 ` Andy Lutomirski
[not found] ` <CALCETrXhXPj_b6rUMn=SR0QwE92rL=k5DCFraZwBj9FpUgadYw@mail.gmail.com>
2016-03-14 18:04 ` Linus Torvalds
[not found] ` <CA+55aFwr80aZ3-1H4VPB5=jeU_Yt=hYFfFvZC5-cNXzgXxGf3A@mail.gmail.com>
2016-03-14 18:10 ` Andy Lutomirski
2016-03-14 18:10 ` Linus Torvalds
[not found] ` <CALCETrV16vh5U0TRzdroSTBR_QHDX1C78t0DDW9qtKjOmV+2sQ@mail.gmail.com>
2016-03-14 18:15 ` Linus Torvalds
[not found] ` <CA+55aFz=PdvMWSsXExrpQC2UV6aLS+=+VOo+K4=njQoU5B9hgA@mail.gmail.com>
2016-03-14 18:24 ` Andy Lutomirski
[not found] ` <CALCETrXAAOcGP7DK+7aKn=2pu=SQ0n_PhG9bV4DcoYcv9epn4A@mail.gmail.com>
2016-03-14 18:40 ` Linus Torvalds
[not found] ` <CA+55aFy2dNgBJwjd+fRUYQf9OxqGkkcjUEarv+o3QSFTJ6+gJQ@mail.gmail.com>
2016-03-14 18:48 ` Andy Lutomirski
[not found] ` <CALCETrWxSBwwFTFsRoR_9AVBoC0iJ1pdWwOq_cnFf3NHUpG4QA@mail.gmail.com>
2016-03-15 10:22 ` Ingo Molnar
[not found] ` <20160315102230.GB23406@gmail.com>
2016-03-15 10:26 ` Ingo Molnar
2016-03-14 20:18 ` Peter Zijlstra
2016-03-15 10:21 ` Ingo Molnar
2016-03-14 14:32 ` [PATCH v4 0/5] [PATCH v3 0/5] Improve non-"safe" MSR access failure handling Boris Ostrovsky
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