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Date: Mon, 14 Mar 2016 11:40:58 -0700
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Subject: Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access
 fails without !panic_on_oops
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@amacapital.net>
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 11:24 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.

And as long as people start understanding that killing the machine is
a bad bad bad thing. It's a debugging nightmare.

               Linus