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 v2 2/6] KVM: arm64: Walk userspace page tables to compute the THP mapping size
Date: Tue, 27 Jul 2021 16:55:42 +0100 [thread overview]
Message-ID: <0cf6325c-a31b-0c0c-41dc-8a62a847a800@arm.com> (raw)
In-Reply-To: <20210726153552.1535838-3-maz@kernel.org>
Hi Marc,
On 7/26/21 4:35 PM, Marc Zyngier wrote:
> We currently rely on the kvm_is_transparent_hugepage() helper to
> discover whether a given page has the potential to be mapped as
> a block mapping.
>
> However, this API doesn't really give un everything we want:
> - we don't get the size: this is not crucial today as we only
> support PMD-sized THPs, but we'd like to have larger sizes
> in the future
> - we're the only user left of the API, and there is a will
> to remove it altogether
>
> To address the above, implement a simple walker using the existing
> page table infrastructure, and plumb it into transparent_hugepage_adjust().
> No new page sizes are supported in the process.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/mmu.c | 34 ++++++++++++++++++++++++++++++----
> 1 file changed, 30 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 3155c9e778f0..0adc1617c557 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -433,6 +433,32 @@ int create_hyp_exec_mappings(phys_addr_t phys_addr, size_t size,
> return 0;
> }
>
> +static struct kvm_pgtable_mm_ops kvm_user_mm_ops = {
> + /* We shouldn't need any other callback to walk the PT */
That looks correct to me, mm_ops is used in __kvm_pgtable_visit(), and then only
the phys_to_virt field callback is used. kvm_host_va() is also the callback used
by kvm_s2_mm_ops, which looks right to me.
> + .phys_to_virt = kvm_host_va,
> +};
> +
> +static int get_user_mapping_size(struct kvm *kvm, u64 addr)
> +{
> + struct kvm_pgtable pgt = {
> + .pgd = (kvm_pte_t *)kvm->mm->pgd,
> + .ia_bits = VA_BITS,
> + .start_level = (KVM_PGTABLE_MAX_LEVELS -
> + CONFIG_PGTABLE_LEVELS),
> + .mm_ops = &kvm_user_mm_ops,
> + };
> + kvm_pte_t pte = 0; /* Keep GCC quiet... */
> + u32 level = ~0;
> + int ret;
> +
> + ret = kvm_pgtable_get_leaf(&pgt, addr, &pte, &level);
> + VM_BUG_ON(ret);
> + VM_BUG_ON(level >= KVM_PGTABLE_MAX_LEVELS);
> + VM_BUG_ON(!(pte & PTE_VALID));
> +
> + return BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(level));
> +}
> +
> static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
> .zalloc_page = stage2_memcache_zalloc_page,
> .zalloc_pages_exact = kvm_host_zalloc_pages_exact,
> @@ -780,7 +806,7 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
> * Returns the size of the mapping.
> */
> static unsigned long
> -transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
> +transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot,
> unsigned long hva, kvm_pfn_t *pfnp,
> phys_addr_t *ipap)
> {
> @@ -791,8 +817,8 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
> * sure that the HVA and IPA are sufficiently aligned and that the
> * block map is contained within the memslot.
> */
> - if (kvm_is_transparent_hugepage(pfn) &&
> - fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) {
> + if (fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE) &&
> + get_user_mapping_size(kvm, hva) >= PMD_SIZE) {
> /*
> * The address we faulted on is backed by a transparent huge
> * page. However, because we map the compound huge page and
> @@ -1051,7 +1077,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> * backed by a THP and thus use block mapping if possible.
> */
> if (vma_pagesize == PAGE_SIZE && !(force_pte || device))
> - vma_pagesize = transparent_hugepage_adjust(memslot, hva,
> + vma_pagesize = transparent_hugepage_adjust(kvm, memslot, hva,
> &pfn, &fault_ipa);
>
> if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
Sean explained well why holding the mmap lock isn't needed here. The patch looks
correct to me:
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Thanks,
Alex
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next prev parent reply other threads:[~2021-07-27 15:56 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-26 15:35 [PATCH v2 0/6] KVM: Remove kvm_is_transparent_hugepage() and friends Marc Zyngier
2021-07-26 15:35 ` [PATCH v2 1/6] KVM: arm64: Introduce helper to retrieve a PTE and its level Marc Zyngier
2021-07-27 10:29 ` Quentin Perret
2021-07-27 15:25 ` Alexandru Elisei
2021-07-28 12:17 ` Marc Zyngier
2021-07-26 15:35 ` [PATCH v2 2/6] KVM: arm64: Walk userspace page tables to compute the THP mapping size Marc Zyngier
2021-07-27 15:55 ` Alexandru Elisei [this message]
2021-07-26 15:35 ` [PATCH v2 3/6] KVM: arm64: Avoid mapping size adjustment on permission fault Marc Zyngier
2021-07-27 16:00 ` Alexandru Elisei
2021-07-26 15:35 ` [PATCH v2 4/6] KVM: Remove kvm_is_transparent_hugepage() and PageTransCompoundMap() Marc Zyngier
2021-07-26 15:35 ` [PATCH v2 5/6] KVM: arm64: Use get_page() instead of kvm_get_pfn() Marc Zyngier
2021-07-27 17:46 ` Alexandru Elisei
2021-07-26 15:35 ` [PATCH v2 6/6] KVM: Get rid " Marc Zyngier
2021-08-02 13:39 ` [PATCH v2 0/6] KVM: Remove kvm_is_transparent_hugepage() and friends Marc Zyngier
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