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SubjectRe: [PATCH] kvm: arm: Enforce PTE mappings at stage2 when needed
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Hi Suzuki,

On 2019/3/12 17:52, Suzuki K Poulose wrote:
> commit 6794ad5443a2118 ("KVM: arm/arm64: Fix unintended stage 2 PMD mappings")
> made the checks to skip huge mappings, stricter. However it introduced
> a bug where we still use huge mappings, ignoring the flag to
> use PTE mappings, by not reseting the vma_pagesize to PAGE_SIZE.
>
> Also, the checks do not cover the PUD huge pages, that was
> under review during the same period. This patch fixes both
> the issues.
>
> Fixes : 6794ad5443a2118 ("KVM: arm/arm64: Fix unintended stage 2 PMD mappings")
> Reported-by: Zenghui Yu <yuzenghui@huawei.com>
> Cc: Zenghui Yu <yuzenghui@huawei.com>
> Cc: Christoffer Dall <christoffer.dall@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---

Thanks for Cc-ing me. It works fine now!


zenghui

> virt/kvm/arm/mmu.c | 43 +++++++++++++++++++++----------------------
> 1 file changed, 21 insertions(+), 22 deletions(-)
>
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 30251e2..66e0fbb5 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -1595,8 +1595,9 @@ static void kvm_send_hwpoison_signal(unsigned long address,
> send_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb, current);
> }
>
> -static bool fault_supports_stage2_pmd_mappings(struct kvm_memory_slot *memslot,
> - unsigned long hva)
> +static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
> + unsigned long hva,
> + unsigned long map_size)
> {
> gpa_t gpa_start, gpa_end;
> hva_t uaddr_start, uaddr_end;
> @@ -1612,34 +1613,34 @@ static bool fault_supports_stage2_pmd_mappings(struct kvm_memory_slot *memslot,
>
> /*
> * Pages belonging to memslots that don't have the same alignment
> - * within a PMD for userspace and IPA cannot be mapped with stage-2
> - * PMD entries, because we'll end up mapping the wrong pages.
> + * within a PMD/PUD for userspace and IPA cannot be mapped with stage-2
> + * PMD/PUD entries, because we'll end up mapping the wrong pages.
> *
> * Consider a layout like the following:
> *
> * memslot->userspace_addr:
> * +-----+--------------------+--------------------+---+
> - * |abcde|fgh Stage-1 PMD | Stage-1 PMD tv|xyz|
> + * |abcde|fgh Stage-1 block | Stage-1 block tv|xyz|
> * +-----+--------------------+--------------------+---+
> *
> * memslot->base_gfn << PAGE_SIZE:
> * +---+--------------------+--------------------+-----+
> - * |abc|def Stage-2 PMD | Stage-2 PMD |tvxyz|
> + * |abc|def Stage-2 block | Stage-2 block |tvxyz|
> * +---+--------------------+--------------------+-----+
> *
> - * If we create those stage-2 PMDs, we'll end up with this incorrect
> + * If we create those stage-2 blocks, we'll end up with this incorrect
> * mapping:
> * d -> f
> * e -> g
> * f -> h
> */
> - if ((gpa_start & ~S2_PMD_MASK) != (uaddr_start & ~S2_PMD_MASK))
> + if ((gpa_start & (map_size - 1)) != (uaddr_start & (map_size - 1)))
> return false;
>
> /*
> * Next, let's make sure we're not trying to map anything not covered
> - * by the memslot. This means we have to prohibit PMD size mappings
> - * for the beginning and end of a non-PMD aligned and non-PMD sized
> + * by the memslot. This means we have to prohibit block size mappings
> + * for the beginning and end of a non-block aligned and non-block sized
> * memory slot (illustrated by the head and tail parts of the
> * userspace view above containing pages 'abcde' and 'xyz',
> * respectively).
> @@ -1648,8 +1649,8 @@ static bool fault_supports_stage2_pmd_mappings(struct kvm_memory_slot *memslot,
> * userspace_addr or the base_gfn, as both are equally aligned (per
> * the check above) and equally sized.
> */
> - return (hva & S2_PMD_MASK) >= uaddr_start &&
> - (hva & S2_PMD_MASK) + S2_PMD_SIZE <= uaddr_end;
> + return (hva & ~(map_size - 1)) >= uaddr_start &&
> + (hva & ~(map_size - 1)) + map_size <= uaddr_end;
> }
>
> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> @@ -1678,12 +1679,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
> }
>
> - if (!fault_supports_stage2_pmd_mappings(memslot, hva))
> - force_pte = true;
> -
> - if (logging_active)
> - force_pte = true;
> -
> /* Let's check if we will get back a huge page backed by hugetlbfs */
> down_read(&current->mm->mmap_sem);
> vma = find_vma_intersection(current->mm, hva, hva + 1);
> @@ -1694,6 +1689,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> }
>
> vma_pagesize = vma_kernel_pagesize(vma);
> + if (logging_active ||
> + !fault_supports_stage2_huge_mapping(memslot, hva, vma_pagesize)) {
> + force_pte = true;
> + vma_pagesize = PAGE_SIZE;
> + }
> +
> /*
> * The stage2 has a minimum of 2 level table (For arm64 see
> * kvm_arm_setup_stage2()). Hence, we are guaranteed that we can
> @@ -1701,11 +1702,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> * As for PUD huge maps, we must make sure that we have at least
> * 3 levels, i.e, PMD is not folded.
> */
> - if ((vma_pagesize == PMD_SIZE ||
> - (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm))) &&
> - !force_pte) {
> + if (vma_pagesize == PMD_SIZE ||
> + (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm)))
> gfn = (fault_ipa & huge_page_mask(hstate_vma(vma))) >> PAGE_SHIFT;
> - }
> up_read(&current->mm->mmap_sem);
>
> /* We need minimum second+third level pages */
>

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