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 <m...@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.eli...@arm.com>
Thanks,
Alex
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