Hi Alex,
On Tue, 01 Sep 2020 14:33:57 +0100,
Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote:
>
> When userspace uses hugetlbfs for the VM memory, user_mem_abort() tries to
> use the same block size to map the faulting IPA in stage 2. If stage 2
> cannot use the same size mapping because the block size doesn't fit in the
> memslot or the memslot is not properly aligned, user_mem_abort() will fall
> back to a page mapping, regardless of the block size. We can do better for
> PUD backed hugetlbfs by checking if a PMD block mapping is possible before
> deciding to use a page.
>
> vma_pagesize is an unsigned long, use 1UL instead of 1ULL when assigning
> its value.
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
> arch/arm64/kvm/mmu.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 25e7dc52c086..f590f7355cda 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1871,15 +1871,24 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> else
> vma_shift = PAGE_SHIFT;
>
> - vma_pagesize = 1ULL << vma_shift;
> if (logging_active ||
> - (vma->vm_flags & VM_PFNMAP) ||
> - !fault_supports_stage2_huge_mapping(memslot, hva, vma_pagesize)) {
> + (vma->vm_flags & VM_PFNMAP)) {
> force_pte = true;
> - vma_pagesize = PAGE_SIZE;
> vma_shift = PAGE_SHIFT;
> }
>
> + if (vma_shift == PUD_SHIFT &&
> + !fault_supports_stage2_huge_mapping(memslot, hva, PUD_SIZE))
> + vma_shift = PMD_SHIFT;
> +
> + if (vma_shift == PMD_SHIFT &&
> + !fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) {
> + force_pte = true;
> + vma_shift = PAGE_SHIFT;
> + }
> +
> + vma_pagesize = 1UL << vma_shift;
> +
> /*
> * The stage2 has a minimum of 2 level table (For arm64 see
> * kvm_arm_setup_stage2()). Hence, we are guaranteed that we can
> @@ -1889,7 +1898,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> */
> 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;
> + gfn = (fault_ipa & ~(vma_pagesize - 1)) >> PAGE_SHIFT;
> mmap_read_unlock(current->mm);
>
> /* We need minimum second+third level pages */
Although this looks like a sensible change, I'm a reluctant to take it
at this stage, given that we already have a bunch of patches from Will
to change the way we deal with PTs.
Could you look into how this could fit into the new code instead?
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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