From: Paolo Bonzini <pbonzini@redhat.com>
To: Chia-I Wu <olvaffe@gmail.com>, kvm@vger.kernel.org
Cc: wanpengli@tencent.com, joro@8bytes.org,
dri-devel@lists.freedesktop.org, gurchetansingh@chromium.org,
kraxel@redhat.com, vkuznets@redhat.com, jmattson@google.com
Subject: Re: [RFC PATCH 1/3] KVM: vmx: rewrite the comment in vmx_get_mt_mask
Date: Fri, 14 Feb 2020 10:36:32 +0100 [thread overview]
Message-ID: <0d88beeb-f960-3d1e-c669-93abe877d8ab@redhat.com> (raw)
In-Reply-To: <20200213213036.207625-2-olvaffe@gmail.com>
On 13/02/20 22:30, Chia-I Wu wrote:
> Better reflect the structure of the code and metion why we could not
> always honor the guest.
>
> Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
> Cc: Gurchetan Singh <gurchetansingh@chromium.org>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> ---
> arch/x86/kvm/vmx/vmx.c | 27 +++++++++++++++++----------
> 1 file changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 3be25ecae145..266ef87042da 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6854,17 +6854,24 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> u8 cache;
> u64 ipat = 0;
>
> - /* For VT-d and EPT combination
> - * 1. MMIO: always map as UC
> - * 2. EPT with VT-d:
> - * a. VT-d without snooping control feature: can't guarantee the
> - * result, try to trust guest.
> - * b. VT-d with snooping control feature: snooping control feature of
> - * VT-d engine can guarantee the cache correctness. Just set it
> - * to WB to keep consistent with host. So the same as item 3.
> - * 3. EPT without VT-d: always map as WB and set IPAT=1 to keep
> - * consistent with host MTRR
> + /* We wanted to honor guest CD/MTRR/PAT, but doing so could result in
> + * memory aliases with conflicting memory types and sometimes MCEs.
> + * We have to be careful as to what are honored and when.
> + *
> + * For MMIO, guest CD/MTRR are ignored. The EPT memory type is set to
> + * UC. The effective memory type is UC or WC depending on guest PAT.
> + * This was historically the source of MCEs and we want to be
> + * conservative.
> + *
> + * When there is no need to deal with noncoherent DMA (e.g., no VT-d
> + * or VT-d has snoop control), guest CD/MTRR/PAT are all ignored. The
> + * EPT memory type is set to WB. The effective memory type is forced
> + * WB.
> + *
> + * Otherwise, we trust guest. Guest CD/MTRR/PAT are all honored. The
> + * EPT memory type is used to emulate guest CD/MTRR.
> */
> +
> if (is_mmio) {
> cache = MTRR_TYPE_UNCACHABLE;
> goto exit;
>
This is certainly an improvement, especially the part that points out
how guest PAT still allows MMIO to be handled as WC.
Thanks,
Paolo
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next prev parent reply other threads:[~2020-02-14 9:36 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-13 21:30 [RFC PATCH 0/3] KVM: x86: honor guest memory type Chia-I Wu
2020-02-13 21:30 ` [RFC PATCH 1/3] KVM: vmx: rewrite the comment in vmx_get_mt_mask Chia-I Wu
2020-02-14 9:36 ` Paolo Bonzini [this message]
2020-02-13 21:30 ` [RFC PATCH 2/3] RFC: KVM: add KVM_MEM_DMA Chia-I Wu
2020-02-13 21:30 ` [RFC PATCH 3/3] RFC: KVM: x86: support KVM_CAP_DMA_MEM Chia-I Wu
2020-02-13 21:41 ` [RFC PATCH 0/3] KVM: x86: honor guest memory type Paolo Bonzini
2020-02-13 22:18 ` Chia-I Wu
2020-02-14 10:26 ` Paolo Bonzini
2020-02-14 19:52 ` Sean Christopherson
2020-02-14 21:47 ` Chia-I Wu
2020-02-14 21:56 ` Jim Mattson
2020-02-14 22:03 ` Sean Christopherson
2020-02-18 16:28 ` Paolo Bonzini
2020-02-18 22:58 ` Sean Christopherson
2020-02-19 9:52 ` Tian, Kevin
2020-02-19 19:36 ` Chia-I Wu
2020-02-20 2:04 ` Tian, Kevin
2020-02-20 2:38 ` Tian, Kevin
2020-02-20 22:23 ` Chia-I Wu
2020-02-21 0:23 ` Tian, Kevin
2020-02-21 4:45 ` Chia-I Wu
2020-02-21 4:51 ` Chia-I Wu
2020-02-21 5:39 ` Tian, Kevin
2020-02-21 15:59 ` Sean Christopherson
2020-02-21 18:21 ` Chia-I Wu
2020-02-25 1:29 ` Tian, Kevin
2020-02-14 21:15 ` Chia-I Wu
2020-02-19 10:00 ` Tian, Kevin
2020-02-19 19:18 ` Chia-I Wu
2020-02-20 2:13 ` Tian, Kevin
2020-02-20 23:02 ` Chia-I Wu
2020-02-24 10:57 ` Gerd Hoffmann
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