[Xen-devel] [PATCH for-xen-4.5] x86/pvh/vpmu: Disable VPMU for PVH guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Currently when VPMU is enabled on a system both HVM and PVH VPCUs will
initialize their VPMUs, including setting up vpmu_ops. As result even
though VPMU will not work for PVH guests (APIC is not supported there),
the guest may decide to perform a write to a PMU MSR. This will cause a
call to is_vlapic_lvtpc_enabled() which will crash the hypervisor, e.g.:

 (XEN) Xen call trace:
 (XEN)    [<ffff82d0801ca06f>] is_vlapic_lvtpc_enabled+0x13/0x22
 (XEN)    [<ffff82d0801e2a15>] core2_vpmu_do_wrmsr+0x415/0x589
 (XEN)    [<ffff82d0801cedaa>] vpmu_do_wrmsr+0x2a/0x33
 (XEN)    [<ffff82d0801dd648>] vmx_msr_write_intercept+0x268/0x557
 (XEN)    [<ffff82d0801bcd2e>] hvm_msr_write_intercept+0x36c/0x39b
 (XEN)    [<ffff82d0801e0a0e>] vmx_vmexit_handler+0x1082/0x185b
 (XEN)    [<ffff82d0801e74c1>] vmx_asm_vmexit_handler+0x41/0xc0

If we prevent VPMU from being initialized on PVH guests we will avoid
those accesses.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vpmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/arch/x86/hvm/vpmu.c b/xen/arch/x86/hvm/vpmu.c
index aec7b5f..4daa993 100644
--- a/xen/arch/x86/hvm/vpmu.c
+++ b/xen/arch/x86/hvm/vpmu.c
@@ -218,6 +218,9 @@ void vpmu_initialise(struct vcpu *v)
     struct vpmu_struct *vpmu = vcpu_vpmu(v);
     uint8_t vendor = current_cpu_data.x86_vendor;
 
+    if ( is_pvh_vcpu(v) )
+        return;
+
     if ( vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) )
         vpmu_destroy(v);
     vpmu_clear(vpmu);
-- 
1.8.1.4


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