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From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 14 Mar 2016 11:48:47 -0700
Message-ID: <CALCETrWxSBwwFTFsRoR_9AVBoC0iJ1pdWwOq_cnFf3NHUpG4QA@mail.gmail.com>
Subject: Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access
 fails without !panic_on_oops
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, xen-devel <Xen-devel@lists.xen.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>, X86 ML <x86@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        KVM list <kvm@vger.kernel.org>, Andy Lutomirski <luto@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
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On Mon, Mar 14, 2016 at 11:40 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Mar 14, 2016 at 11:24 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>>
>> 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);
>
> I guess I can live with this, as long as we also extend the
> early-fault handling to work with the special exception handlers.

OK, will do.  I need to rewrork the early IDT code a bit so it
generates a real pt_regs layout, but that's arguably a cleanup anyway.

--Andy