KVM: SVM: Fake MSR_K7 performance counters
authorChris Lalancette <clalance@redhat.com>
Mon, 5 May 2008 17:05:16 +0000 (13:05 -0400)
committerAvi Kivity <avi@qumranet.com>
Sun, 20 Jul 2008 09:40:49 +0000 (12:40 +0300)
commit14ae51b6c068ef7ab52dc2d53fe226e6189f2ab2
tree1abe5475c427980663865a0231198c7a20afe1dc
parentf697554515b06e8d7264f316b25e6da943407142
KVM: SVM: Fake MSR_K7 performance counters

Attached is a patch that fixes a guest crash when booting older Linux kernels.
The problem stems from the fact that we are currently emulating
MSR_K7_EVNTSEL[0-3], but not emulating MSR_K7_PERFCTR[0-3].  Because of this,
setup_k7_watchdog() in the Linux kernel receives a GPF when it attempts to
write into MSR_K7_PERFCTR, which causes an OOPs.

The patch fixes it by just "fake" emulating the appropriate MSRs, throwing
away the data in the process.  This causes the NMI watchdog to not actually
work, but it's not such a big deal in a virtualized environment.

When we get a write to one of these counters, we printk_ratelimit() a warning.
I decided to print it out for all writes, even if the data is 0; it doesn't
seem to make sense to me to special case when data == 0.

Tested by myself on a RHEL-4 guest, and Joerg Roedel on a Windows XP 64-bit
guest.

Signed-off-by: Chris Lalancette <clalance@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
arch/x86/kvm/svm.c