On Wed, Jul 09, 2014 at 03:43:45PM +0000, Liang, Kan wrote: > > > > -----Original Message----- > > From: Peter Zijlstra [mailto:[email protected]] > > Sent: Wednesday, July 09, 2014 10:58 AM > > To: Liang, Kan > > Cc: [email protected]; [email protected]; [email protected] > > Subject: Re: [PATCH V4 1/2] perf ignore LBR and extra_regs. > > > > On Wed, Jul 09, 2014 at 02:32:28PM +0000, Liang, Kan wrote: > > > > > > > > > > On Tue, Jul 08, 2014 at 09:49:40AM -0700, [email protected] wrote: > > > > > +/* > > > > > + * Under certain circumstances, access certain MSR may cause #GP. > > > > > + * The function tests if the input MSR can be safely accessed. > > > > > + */ > > > > > +static inline bool check_msr(unsigned long msr) { > > > > > + u64 value; > > > > > + > > > > > + if (rdmsrl_safe(msr, &value) < 0) > > > > > + return false; > > > > > + if (wrmsrl_safe(msr, value) < 0) > > > > > + return false; > > > > > + return true; > > > > > +} > > > > > > > > What does this thing return after patch 2? does the write still > > > > fault or will KVM silently take writes too? > > > > > > If applying patch 2, the function will return true. The KVM just simply > > > ignore > > the reads/writes. > > > > OK, then that's broken too. We want a function to return false for any > > malfunctioning MSR, ignoring writes and returning 0s is not proper > > functioning. > > The patch 2 is to handle the case that the administrator can only > patch the host. Don't need to force user to upgrade their guest to fix > the crash. And ignore the annoying "unhandled...." KVM messages
Sure; but what I meant was, check_msr() is broken when ran on such a kernel. You need to fix check_msr() to return failure on these 'ignored' MSRs, after all they don't function as expected, they're effectively broken.
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