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Re: [Xen-devel] [PATCH v6 11/19] x86/VPMU: Initialize PMU for PV guests

On 05/21/2014 04:01 AM, Jan Beulich wrote:
On 20.05.14 at 19:47, <boris.ostrovsky@xxxxxxxxxx> wrote:
On 05/20/2014 11:51 AM, Jan Beulich wrote:
On 13.05.14 at 17:53, <boris.ostrovsky@xxxxxxxxxx> wrote:
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1150,7 +1150,8 @@ static int svm_vcpu_initialise(struct vcpu *v)
           return rc;
- vpmu_initialise(v);
+    if ( is_hvm_domain(v->domain) )
+        vpmu_initialise(v);
This patch adds initialization for PV domains, which is conditioned by
is_pv_domain() in amd_vpmu_initialise()/core2_vpmu_alloc_resource(). I
don't want PVH domains (which call these routines) to try to set up
their VPMUs from here. This is supposed to happen via pvpmu_init()
(which in this patch will return -EINVAL for PVH).
So what's the reason for making PVH PV-like here rather than
HVM-like? With the intended goal of making PVH a HVM sub-mode,
that'll require more exceptions in the long run.

Primarily because of interrupt handling: we don't end up in HVM guest's interrupt handler for PMU interrupts but rather in the PV PMU_VIRQ handler which expects shared context to be set up. This means that initialization for PVH has to be slightly different.


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