[PATCH v2 0/9] arm64: KVM: Fix PMU exception generation

On Mon, Mar 27, 2017 at 05:03:36PM +0100, Marc Zyngier wrote:

Running the following code:

root at zomby-woof:~# cat test-pmu.c
int main(int argc, char *argv[])
{
	unsigned int val;
	asm ("mrc p15, 0, %0, c9, c13, 0\n" : "=r" (val));
	return val;
}

in a 32bit guest (or a 64bit guest with a 32bit userspace) results in
this surprising result:

[  120.347497] kvm [1150]: Unsupported guest CP15 access at: ab0945ae
[  120.353689] kvm [1142]:  { Op0( 0), Op1( 0), CRn( 9), CRm(13), Op2( 0), func_read },

which is weird, because the guest behaves correctly:
root at zomby-woof:~# ./test-pmu 
[   16.184422] test-pmu[740]: undefined instruction: pc=00000000ab0945ae
[   16.186043] Code: 00340001 b4800000 af00b085 60396078 (3f1dee19) 
Illegal instruction

It gets the expected UNDEF, and all is fine. So what?

It turns out that the PMU emulation code is a bit lazy, and tells the
rest of KVM that the emulation has failed, so that an exception gets
delivered. Subtle differences in the 32bit vs 64bit handling make it
spit an "Unsupported..." error.

This series tries to set things straight:
- Make all PMU illegal accesses inject an UNDEF
- Make these illegal accesses a successful emulation w.r.t the rest of KVM.

In the process, we also squash an interesting bug in the 64bit CP
access. Similar treatment is applied to the 32bit kernel, except that
we don't ever inject an exception there (no PMU support yet).

I have applied this series to queue (not next since I haven't tested
thoroughly yet), with the fixups agreed in the series.

Thanks,
-Christoffer