From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: KVM list <kvm@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
xen-devel <Xen-devel@lists.xen.org>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.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 11:24:00 -0700 [thread overview]
Message-ID: <CALCETrXAAOcGP7DK+7aKn=2pu=SQ0n_PhG9bV4DcoYcv9epn4A__4987.89430498636$1457979947$gmane$org@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFz=PdvMWSsXExrpQC2UV6aLS+=+VOo+K4=njQoU5B9hgA@mail.gmail.com>
On Mon, Mar 14, 2016 at 11:15 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Mar 14, 2016 at 11:10 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>>
>> A couple of the wrmsr users actually care about performance. These
>> are the ones involved in context switching and, to a lesser extent, in
>> switching in and out of guest mode.
>
> .. ok, see the crossed emails.
>
> I'd *much* rather special case the special cases. Not make the generic
> case something complex.
The code in my queue is, literally:
bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
struct pt_regs *regs, int trapnr)
{
WARN_ONCE(1, "unchecked MSR access error: RDMSR from 0x%x",
(unsigned int)regs->cx);
/* Pretend that the read succeeded and returned 0. */
regs->ip = ex_fixup_addr(fixup);
regs->ax = 0;
regs->dx = 0;
return true;
}
EXPORT_SYMBOL(ex_handler_rdmsr_unsafe);
The only regard in which this is any more complex than the _safe
variant is because there's a warning (one line of code) and because
the _safe variant forgot to zero the result (two lines of code). My
series fixes the latter, so we're talking about almost no source code
size difference. There *is* a difference in binary size, though --
the _safe variant emits a copy of its fixup every time it appears,
whereas the new fixup appears once.
So I think we should apply my patches (with the early handling fixed
and the panic_on_oops removed), and then consider reimplementing the
_safe variant using fancy handlers to reduce number of lines of asm
and code size, and then consider changing the overall API on top if we
think there's a better API to be had.
Is that okay?
>
> And *particularly* not make the generic case be something where people
> think it's sane to oops and kill the machine. Christ.
I've already removed the panic_on_oops thing from my tree.
--Andy
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next prev parent reply other threads:[~2016-03-14 18:24 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 ` [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Borislav Petkov
[not found] ` <20160314120202.GD15800@pd.tnic>
2016-03-14 17:05 ` 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 [this message]
[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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