KVM Archive on lore.kernel.org
 help / color / Atom feed
* [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	[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

end of thread, back to index

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
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

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org kvm@archiver.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/ public-inbox