FAILED: patch "[PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit" failed to apply to 4.19-stable tree

FAILED: patch "[PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit" failed to apply to 4.19-stable tree

[gregkh]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b6b80c78af838bef17501416d5d383fedab0010a Mon Sep 17 00:00:00 2001
From: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Thu, 13 Jun 2019 10:22:23 -0700
Subject: [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit
 NPT

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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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;

[PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT

[Jiri Palecek]

Original commit id b6b80c78 ported to stable/linux-4.19.y.

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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 779ed52047d1..e0f982e35c96 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5386,7 +5386,16 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
 	struct page *page;
 	int i;

-	if (tdp_enabled)
+	/*
+	 * 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;

 	/*
--
2.20.1

Re: [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT

[Sasha Levin]

On Tue, Jun 25, 2019 at 12:45:24PM +0200, Jiri Palecek wrote:
>Original commit id b6b80c78 ported to stable/linux-4.19.y.
>
>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>
>Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Could you add your signed-off-by please?

--
Thanks,
Sasha

[PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT

[Sean Christopherson]

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

Re: [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT

[Jiri Palecek]

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;

Re: [PATCH] KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT

[Paolo Bonzini]

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