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From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	kvmarm@lists.cs.columbia.edu, linux-mm@kvack.org
Cc: Sean Christopherson <seanjc@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Will Deacon <will@kernel.org>,
	Quentin Perret <qperret@google.com>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kernel-team@android.com
Subject: Re: [PATCH 2/5] KVM: arm64: Avoid mapping size adjustment on permission fault
Date: Fri, 23 Jul 2021 16:55:39 +0100	[thread overview]
Message-ID: <a8f42fdf-4cbc-ad10-c8cc-cbbf850f85e4@arm.com> (raw)
In-Reply-To: <20210717095541.1486210-3-maz@kernel.org>

Hi Marc,

On 7/17/21 10:55 AM, Marc Zyngier wrote:
> Since we only support PMD-sized mappings for THP, getting
> a permission fault on a level that results in a mapping
> being larger than PAGE_SIZE is a sure indication that we have
> already upgraded our mapping to a PMD.
>
> In this case, there is no need to try and parse userspace page
> tables, as the fault information already tells us everything.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/mmu.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index db6314b93e99..c036a480ca27 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1088,9 +1088,14 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	 * If we are not forced to use page mapping, check if we are
>  	 * backed by a THP and thus use block mapping if possible.
>  	 */
> -	if (vma_pagesize == PAGE_SIZE && !(force_pte || device))
> -		vma_pagesize = transparent_hugepage_adjust(kvm, memslot, hva,
> -							   &pfn, &fault_ipa);
> +	if (vma_pagesize == PAGE_SIZE && !force_pte) {

Looks like now it's possible to call transparent_hugepage_adjust() for devices (if
fault_status != FSC_PERM). Commit 2aa53d68cee6 ("KVM: arm64: Try stage2 block
mapping for host device MMIO") makes a good case for the !device check. Was the
check removed unintentionally?

> +		if (fault_status == FSC_PERM && fault_granule > PAGE_SIZE)
> +			vma_pagesize = fault_granule;
> +		else
> +			vma_pagesize = transparent_hugepage_adjust(kvm, memslot,
> +								   hva, &pfn,
> +								   &fault_ipa);
> +	}

This change makes sense to me - we can only get stage 2 permission faults on a
leaf entry since stage 2 tables don't have the APTable/XNTable/PXNTable bits. The
biggest block mapping size that we support at stage 2 is PMD size (from
transparent_hugepage_adjust()), therefore if fault_granule is larger than
PAGE_SIZE, then it must be PMD_SIZE.

Thanks,

Alex

>  
>  	if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
>  		/* Check the VMM hasn't introduced a new VM_SHARED VMA */

WARNING: multiple messages have this Message-ID
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	kvmarm@lists.cs.columbia.edu, linux-mm@kvack.org
Cc: kernel-team@android.com, Sean Christopherson <seanjc@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH 2/5] KVM: arm64: Avoid mapping size adjustment on permission fault
Date: Fri, 23 Jul 2021 16:55:39 +0100	[thread overview]
Message-ID: <a8f42fdf-4cbc-ad10-c8cc-cbbf850f85e4@arm.com> (raw)
In-Reply-To: <20210717095541.1486210-3-maz@kernel.org>

Hi Marc,

On 7/17/21 10:55 AM, Marc Zyngier wrote:
> Since we only support PMD-sized mappings for THP, getting
> a permission fault on a level that results in a mapping
> being larger than PAGE_SIZE is a sure indication that we have
> already upgraded our mapping to a PMD.
>
> In this case, there is no need to try and parse userspace page
> tables, as the fault information already tells us everything.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/mmu.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index db6314b93e99..c036a480ca27 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1088,9 +1088,14 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	 * If we are not forced to use page mapping, check if we are
>  	 * backed by a THP and thus use block mapping if possible.
>  	 */
> -	if (vma_pagesize == PAGE_SIZE && !(force_pte || device))
> -		vma_pagesize = transparent_hugepage_adjust(kvm, memslot, hva,
> -							   &pfn, &fault_ipa);
> +	if (vma_pagesize == PAGE_SIZE && !force_pte) {

Looks like now it's possible to call transparent_hugepage_adjust() for devices (if
fault_status != FSC_PERM). Commit 2aa53d68cee6 ("KVM: arm64: Try stage2 block
mapping for host device MMIO") makes a good case for the !device check. Was the
check removed unintentionally?

> +		if (fault_status == FSC_PERM && fault_granule > PAGE_SIZE)
> +			vma_pagesize = fault_granule;
> +		else
> +			vma_pagesize = transparent_hugepage_adjust(kvm, memslot,
> +								   hva, &pfn,
> +								   &fault_ipa);
> +	}

This change makes sense to me - we can only get stage 2 permission faults on a
leaf entry since stage 2 tables don't have the APTable/XNTable/PXNTable bits. The
biggest block mapping size that we support at stage 2 is PMD size (from
transparent_hugepage_adjust()), therefore if fault_granule is larger than
PAGE_SIZE, then it must be PMD_SIZE.

Thanks,

Alex

>  
>  	if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
>  		/* Check the VMM hasn't introduced a new VM_SHARED VMA */
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	kvmarm@lists.cs.columbia.edu, linux-mm@kvack.org
Cc: Sean Christopherson <seanjc@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Will Deacon <will@kernel.org>,
	Quentin Perret <qperret@google.com>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kernel-team@android.com
Subject: Re: [PATCH 2/5] KVM: arm64: Avoid mapping size adjustment on permission fault
Date: Fri, 23 Jul 2021 16:55:39 +0100	[thread overview]
Message-ID: <a8f42fdf-4cbc-ad10-c8cc-cbbf850f85e4@arm.com> (raw)
In-Reply-To: <20210717095541.1486210-3-maz@kernel.org>

Hi Marc,

On 7/17/21 10:55 AM, Marc Zyngier wrote:
> Since we only support PMD-sized mappings for THP, getting
> a permission fault on a level that results in a mapping
> being larger than PAGE_SIZE is a sure indication that we have
> already upgraded our mapping to a PMD.
>
> In this case, there is no need to try and parse userspace page
> tables, as the fault information already tells us everything.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/mmu.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index db6314b93e99..c036a480ca27 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1088,9 +1088,14 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	 * If we are not forced to use page mapping, check if we are
>  	 * backed by a THP and thus use block mapping if possible.
>  	 */
> -	if (vma_pagesize == PAGE_SIZE && !(force_pte || device))
> -		vma_pagesize = transparent_hugepage_adjust(kvm, memslot, hva,
> -							   &pfn, &fault_ipa);
> +	if (vma_pagesize == PAGE_SIZE && !force_pte) {

Looks like now it's possible to call transparent_hugepage_adjust() for devices (if
fault_status != FSC_PERM). Commit 2aa53d68cee6 ("KVM: arm64: Try stage2 block
mapping for host device MMIO") makes a good case for the !device check. Was the
check removed unintentionally?

> +		if (fault_status == FSC_PERM && fault_granule > PAGE_SIZE)
> +			vma_pagesize = fault_granule;
> +		else
> +			vma_pagesize = transparent_hugepage_adjust(kvm, memslot,
> +								   hva, &pfn,
> +								   &fault_ipa);
> +	}

This change makes sense to me - we can only get stage 2 permission faults on a
leaf entry since stage 2 tables don't have the APTable/XNTable/PXNTable bits. The
biggest block mapping size that we support at stage 2 is PMD size (from
transparent_hugepage_adjust()), therefore if fault_granule is larger than
PAGE_SIZE, then it must be PMD_SIZE.

Thanks,

Alex

>  
>  	if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
>  		/* Check the VMM hasn't introduced a new VM_SHARED VMA */

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-07-23 15:55 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-17  9:55 [PATCH 0/5] KVM: Remove kvm_is_transparent_hugepage() and friends Marc Zyngier
2021-07-17  9:55 ` Marc Zyngier
2021-07-17  9:55 ` Marc Zyngier
2021-07-17  9:55 ` [PATCH 1/5] KVM: arm64: Walk userspace page tables to compute the THP mapping size Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-19  6:31   ` Paolo Bonzini
2021-07-19  6:31     ` Paolo Bonzini
2021-07-19  6:31     ` Paolo Bonzini
2021-07-19  9:31     ` Marc Zyngier
2021-07-19  9:31       ` Marc Zyngier
2021-07-19  9:31       ` Marc Zyngier
2021-07-20 17:23   ` Alexandru Elisei
2021-07-20 17:23     ` Alexandru Elisei
2021-07-20 17:23     ` Alexandru Elisei
2021-07-20 20:33     ` Sean Christopherson
2021-07-20 20:33       ` Sean Christopherson
2021-07-20 20:33       ` Sean Christopherson
2021-07-21 14:58       ` Will Deacon
2021-07-21 14:58         ` Will Deacon
2021-07-21 14:58         ` Will Deacon
2021-07-21 15:56         ` Sean Christopherson
2021-07-21 15:56           ` Sean Christopherson
2021-07-21 15:56           ` Sean Christopherson
2021-07-21 16:37       ` Alexandru Elisei
2021-07-21 16:37         ` Alexandru Elisei
2021-07-21 16:37         ` Alexandru Elisei
2021-07-23  8:48     ` Marc Zyngier
2021-07-23  8:48       ` Marc Zyngier
2021-07-23  8:48       ` Marc Zyngier
2021-07-17  9:55 ` [PATCH 2/5] KVM: arm64: Avoid mapping size adjustment on permission fault Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-23 15:55   ` Alexandru Elisei [this message]
2021-07-23 15:55     ` Alexandru Elisei
2021-07-23 15:55     ` Alexandru Elisei
2021-07-23 16:18     ` Marc Zyngier
2021-07-23 16:18       ` Marc Zyngier
2021-07-23 16:18       ` Marc Zyngier
2021-07-17  9:55 ` [PATCH 3/5] KVM: Remove kvm_is_transparent_hugepage() and PageTransCompoundMap() Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-19  6:31   ` Paolo Bonzini
2021-07-19  6:31     ` Paolo Bonzini
2021-07-19  6:31     ` Paolo Bonzini
2021-07-17  9:55 ` [PATCH 4/5] KVM: arm64: Use get_page() instead of kvm_get_pfn() Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-17  9:55 ` [PATCH 5/5] KVM: Get rid " Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-17  9:55   ` Marc Zyngier
2021-07-19  6:31   ` Paolo Bonzini
2021-07-19  6:31     ` Paolo Bonzini
2021-07-19  6:31     ` Paolo Bonzini

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