linux-kernel - Re: [PATCH v3 06/15] KVM: arm64: Implement kvm_pgtable_hyp

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Date:   Tue, 7 Dec 2021 14:47:14 +0000
From:   Andrew Walbran <qwandor@...gle.com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 06/15] KVM: arm64: Implement kvm_pgtable_hyp_unmap() at EL2

On Wed, 1 Dec 2021 at 17:04, 'Quentin Perret' via kernel-team
<kernel-team@...roid.com> wrote:
>
> From: Will Deacon <will@...nel.org>
>
> Implement kvm_pgtable_hyp_unmap() which can be used to remove hypervisor
> stage-1 mappings at EL2.
>
> Signed-off-by: Will Deacon <will@...nel.org>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 21 ++++++++++
>  arch/arm64/kvm/hyp/pgtable.c         | 63 ++++++++++++++++++++++++++++
>  2 files changed, 84 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 027783829584..9d076f36401d 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -251,6 +251,27 @@ void kvm_pgtable_hyp_destroy(struct kvm_pgtable *pgt);
>  int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys,
>                         enum kvm_pgtable_prot prot);
>
> +/**
> + * kvm_pgtable_hyp_unmap() - Remove a mapping from a hypervisor stage-1 page-table.
> + * @pgt:       Page-table structure initialised by kvm_pgtable_hyp_init().
> + * @addr:      Virtual address from which to remove the mapping.
> + * @size:      Size of the mapping.
> + *
> + * The offset of @addr within a page is ignored, @size is rounded-up to
> + * the next page boundary and @phys is rounded-down to the previous page
> + * boundary.
> + *
> + * TLB invalidation is performed for each page-table entry cleared during the
> + * unmapping operation and the reference count for the page-table page
> + * containing the cleared entry is decremented, with unreferenced pages being
> + * freed. The unmapping operation will stop early if it encounters either an
> + * invalid page-table entry or a valid block mapping which maps beyond the range
> + * being unmapped.

How is the caller expected to break up the block mapping? Why not
handle that within this function?

>
> + *
> + * Return: Number of bytes unmapped, which may be 0.
> + */
> +u64 kvm_pgtable_hyp_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size);
> +
>  /**
>   * kvm_get_vtcr() - Helper to construct VTCR_EL2
>   * @mmfr0:     Sanitized value of SYS_ID_AA64MMFR0_EL1 register.
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 768a58835153..6ad4cb2d6947 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -463,6 +463,69 @@ int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys,
>         return ret;
>  }
>
> +struct hyp_unmap_data {
> +       u64                             unmapped;
> +       struct kvm_pgtable_mm_ops       *mm_ops;
> +};
> +
> +static int hyp_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> +                           enum kvm_pgtable_walk_flags flag, void * const arg)
> +{
> +       kvm_pte_t pte = *ptep, *childp = NULL;
> +       u64 granule = kvm_granule_size(level);
> +       struct hyp_unmap_data *data = arg;
> +       struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
> +
> +       if (!kvm_pte_valid(pte))
> +               return -EINVAL;
> +
> +       if (kvm_pte_table(pte, level)) {
> +               childp = kvm_pte_follow(pte, mm_ops);
> +
> +               if (mm_ops->page_count(childp) != 1)
> +                       return 0;
> +
> +               kvm_clear_pte(ptep);
> +               dsb(ishst);
> +               __tlbi_level(vae2is, __TLBI_VADDR(addr, 0), level);
> +       } else {
> +               if (end - addr < granule)
> +                       return -EINVAL;
> +
> +               kvm_clear_pte(ptep);
> +               dsb(ishst);
> +               __tlbi_level(vale2is, __TLBI_VADDR(addr, 0), level);
> +               data->unmapped += granule;
> +       }
> +
> +       dsb(ish);
> +       isb();
> +       mm_ops->put_page(ptep);
> +
> +       if (childp)
> +               mm_ops->put_page(childp);
> +
> +       return 0;
> +}
> +
> +u64 kvm_pgtable_hyp_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
> +{
> +       struct hyp_unmap_data unmap_data = {
> +               .mm_ops = pgt->mm_ops,
> +       };
> +       struct kvm_pgtable_walker walker = {
> +               .cb     = hyp_unmap_walker,
> +               .arg    = &unmap_data,
> +               .flags  = KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
> +       };
> +
> +       if (!pgt->mm_ops->page_count)
> +               return 0;
> +
> +       kvm_pgtable_walk(pgt, addr, size, &walker);
> +       return unmap_data.unmapped;
> +}
> +
>  int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
>                          struct kvm_pgtable_mm_ops *mm_ops)
>  {
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>
> --
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>

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