On 02/09/2015 21:01, Sebastian Schütte wrote:
> I inserted some printk() lines into init_vmcb() around the call of
> svm_set_guest_pat() to print out the g_pat value as well as
> svm->vcpu.vcpu_id and noticed that something was off:
>
> Initially, the PATs of all VCPUs are set to 0x0606060606060606.
> However, after attaching some devices (vfio-pci enabling device and
> vfio_ecap_init lines are being printed) init_vmcb() is only called
> again for vcpu_id > 0. Unless g_pat is changed somewhere else, VCPU
> #0 remains set to 0x0606060606060606 (according to comments in
> svm_set_guest_pat() this is bad for assigned devices) while all other
> VCPUs use 0x0007040600070406.
>
> I'd guess that could explain the slowdown.
>
Hi, sorry for the delay. If you change KVM like this
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 27f57fc05bc7..3ce878c5fde8 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1155,10 +1155,7 @@ static void svm_set_guest_pat(struct vcpu_svm *svm, u64
*g_pat)
* have assigned devices, however, we cannot force WB for RAM
* pages only, so use the guest PAT directly.
*/
- if (!kvm_arch_has_assigned_device(vcpu->kvm))
- *g_pat = 0x0606060606060606;
- else
- *g_pat = vcpu->arch.pat;
+ *g_pat = vcpu->arch.pat;
}
static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
(obviously not a valid patch for upstream patch, but good enough for
testing) do you get normal speed?
Paolo
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