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SubjectRe: [PATCH] KVM: x86: Work around buggy MPX platform
Il 10/03/2014 09:48, Liu, Jinsong ha scritto:
> From 5854070994c5002b3a37577165ed3e82f36f712d Mon Sep 17 00:00:00 2001
> From: Liu Jinsong <jinsong.liu@intel.com>
> Date: Sat, 8 Mar 2014 04:40:02 +0800
> Subject: [PATCH] KVM: x86: Work around buggy MPX platform
>
> Work around buggy MPX platform which support MSR_IA32_BNDCFGS
> but has issue at, say, VMX ucode.
>
> Signed-off-by: Liu Jinsong <jinsong.liu@intel.com>
> ---
> arch/x86/kvm/x86.c | 14 +++++++++++++-
> 1 files changed, 13 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1e91a24..1fc184d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3936,6 +3936,16 @@ static void kvm_init_msr_list(void)
> for (i = j = KVM_SAVE_MSRS_BEGIN; i < ARRAY_SIZE(msrs_to_save); i++) {
> if (rdmsr_safe(msrs_to_save[i], &dummy[0], &dummy[1]) < 0)
> continue;
> +
> + /*
> + * Work around some buggy MPX platform which support
> + * MSR_IA32_BNDCFGS but has issue at, say, VMX ucode.
> + */
> + if ((msrs_to_save[i] == MSR_IA32_BNDCFGS) &&

Too many parentheses in this "if".


> + (kvm_x86_ops->mpx_supported ?
> + !kvm_x86_ops->mpx_supported() : 1))

Better: "!kvm_x86_ops->mpx_supported || !kvm_x86_ops->mpx_supported()"
but I'm leaning towards adding an implementation of mpx_supported to SVM
too (it will always return false).

> + continue;
> +
> if (j < i)
> msrs_to_save[j] = msrs_to_save[i];
> j++;
> @@ -5576,9 +5586,11 @@ int kvm_arch_init(void *opaque)
> goto out_free_percpu;
>
> kvm_set_mmio_spte_mask();
> - kvm_init_msr_list();
>
> kvm_x86_ops = ops;
> +
> + kvm_init_msr_list();
> +
> kvm_mmu_set_mask_ptes(PT_USER_MASK, PT_ACCESSED_MASK,
> PT_DIRTY_MASK, PT64_NX_MASK, 0);
>
>

Thanks Liu. Indeed I could not reproduce Robert's issue, though it
might be possible to get it with nested virtualization. I'll send a
similar patch that I was testing.

Paolo


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