* [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT
@ 2019-06-13 17:22 Sean Christopherson
2019-06-17 13:07 ` Jiri Palecek
2019-06-18 17:04 ` Paolo Bonzini
0 siblings, 2 replies; 3+ messages in thread
From: Sean Christopherson @ 2019-06-13 17:22 UTC (permalink / raw)
To: Paolo Bonzini, Radim Krčmář; +Cc: kvm, Jiri Palecek
SVM's Nested Page Tables (NPT) reuses x86 paging for the host-controlled
page walk. For 32-bit KVM, this means PAE paging is used even when TDP
is enabled, i.e. the PAE root array needs to be allocated.
Fixes: ee6268ba3a68 ("KVM: x86: Skip pae_root shadow allocation if tdp enabled")
Cc: stable@vger.kernel.org
Reported-by: Jiri Palecek <jpalecek@web.de>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
Jiri, can you please test this patch? I haven't actually verified this
fixes the bug due to lack of SVM hardware.
arch/x86/kvm/mmu.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 1e9ba81accba..d3c3d5e5ffd4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5602,14 +5602,18 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
struct page *page;
int i;
- if (tdp_enabled)
- return 0;
-
/*
- * When emulating 32-bit mode, cr3 is only 32 bits even on x86_64.
- * Therefore we need to allocate shadow page tables in the first
- * 4GB of memory, which happens to fit the DMA32 zone.
+ * When using PAE paging, the four PDPTEs are treated as 'root' pages,
+ * while the PDP table is a per-vCPU construct that's allocated at MMU
+ * creation. When emulating 32-bit mode, cr3 is only 32 bits even on
+ * x86_64. Therefore we need to allocate the PDP table in the first
+ * 4GB of memory, which happens to fit the DMA32 zone. Except for
+ * SVM's 32-bit NPT support, TDP paging doesn't use PAE paging and can
+ * skip allocating the PDP table.
*/
+ if (tdp_enabled && kvm_x86_ops->get_tdp_level(vcpu) > PT32E_ROOT_LEVEL)
+ return 0;
+
page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_DMA32);
if (!page)
return -ENOMEM;
--
2.21.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT
2019-06-13 17:22 [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT Sean Christopherson
@ 2019-06-17 13:07 ` Jiri Palecek
2019-06-18 17:04 ` Paolo Bonzini
1 sibling, 0 replies; 3+ messages in thread
From: Jiri Palecek @ 2019-06-17 13:07 UTC (permalink / raw)
To: Sean Christopherson, Paolo Bonzini, Radim Krčmář; +Cc: kvm
Hello,
On 13. 06. 19 19:22, Sean Christopherson wrote:
> SVM's Nested Page Tables (NPT) reuses x86 paging for the host-controlled
> page walk. For 32-bit KVM, this means PAE paging is used even when TDP
> is enabled, i.e. the PAE root array needs to be allocated.
>
> Fixes: ee6268ba3a68 ("KVM: x86: Skip pae_root shadow allocation if tdp enabled")
> Cc: stable@vger.kernel.org
> Reported-by: Jiri Palecek <jpalecek@web.de>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>
> Jiri, can you please test this patch? I haven't actually verified this
> fixes the bug due to lack of SVM hardware.
Yes, it makes KVM work again on i686 pae and nopae with kernel 5.2-rc4.
However, I also tried, just out of curiosity, a nested kvm setup and got
a kvm_spurious_fault in L1 every time. I'll probably file another bug
for that.
Thanks for your involvement
Jiri Palecek
>
> arch/x86/kvm/mmu.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 1e9ba81accba..d3c3d5e5ffd4 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -5602,14 +5602,18 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
> struct page *page;
> int i;
>
> - if (tdp_enabled)
> - return 0;
> -
> /*
> - * When emulating 32-bit mode, cr3 is only 32 bits even on x86_64.
> - * Therefore we need to allocate shadow page tables in the first
> - * 4GB of memory, which happens to fit the DMA32 zone.
> + * When using PAE paging, the four PDPTEs are treated as 'root' pages,
> + * while the PDP table is a per-vCPU construct that's allocated at MMU
> + * creation. When emulating 32-bit mode, cr3 is only 32 bits even on
> + * x86_64. Therefore we need to allocate the PDP table in the first
> + * 4GB of memory, which happens to fit the DMA32 zone. Except for
> + * SVM's 32-bit NPT support, TDP paging doesn't use PAE paging and can
> + * skip allocating the PDP table.
> */
> + if (tdp_enabled && kvm_x86_ops->get_tdp_level(vcpu) > PT32E_ROOT_LEVEL)
> + return 0;
> +
> page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_DMA32);
> if (!page)
> return -ENOMEM;
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT
2019-06-13 17:22 [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT Sean Christopherson
2019-06-17 13:07 ` Jiri Palecek
@ 2019-06-18 17:04 ` Paolo Bonzini
1 sibling, 0 replies; 3+ messages in thread
From: Paolo Bonzini @ 2019-06-18 17:04 UTC (permalink / raw)
To: Sean Christopherson, Radim Krčmář; +Cc: kvm, Jiri Palecek
On 13/06/19 19:22, Sean Christopherson wrote:
> SVM's Nested Page Tables (NPT) reuses x86 paging for the host-controlled
> page walk. For 32-bit KVM, this means PAE paging is used even when TDP
> is enabled, i.e. the PAE root array needs to be allocated.
>
> Fixes: ee6268ba3a68 ("KVM: x86: Skip pae_root shadow allocation if tdp enabled")
> Cc: stable@vger.kernel.org
> Reported-by: Jiri Palecek <jpalecek@web.de>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>
> Jiri, can you please test this patch? I haven't actually verified this
> fixes the bug due to lack of SVM hardware.
>
> arch/x86/kvm/mmu.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 1e9ba81accba..d3c3d5e5ffd4 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -5602,14 +5602,18 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
> struct page *page;
> int i;
>
> - if (tdp_enabled)
> - return 0;
> -
> /*
> - * When emulating 32-bit mode, cr3 is only 32 bits even on x86_64.
> - * Therefore we need to allocate shadow page tables in the first
> - * 4GB of memory, which happens to fit the DMA32 zone.
> + * When using PAE paging, the four PDPTEs are treated as 'root' pages,
> + * while the PDP table is a per-vCPU construct that's allocated at MMU
> + * creation. When emulating 32-bit mode, cr3 is only 32 bits even on
> + * x86_64. Therefore we need to allocate the PDP table in the first
> + * 4GB of memory, which happens to fit the DMA32 zone. Except for
> + * SVM's 32-bit NPT support, TDP paging doesn't use PAE paging and can
> + * skip allocating the PDP table.
> */
> + if (tdp_enabled && kvm_x86_ops->get_tdp_level(vcpu) > PT32E_ROOT_LEVEL)
> + return 0;
> +
> page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_DMA32);
> if (!page)
> return -ENOMEM;
>
Queued, thanks.
Paolo
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-06-13 17:22 [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT Sean Christopherson
2019-06-17 13:07 ` Jiri Palecek
2019-06-18 17:04 ` Paolo Bonzini
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