On 03/10/13 21:36, Christoffer Dall wrote:
> Support transparent huge pages in KVM/ARM and KVM/ARM64. The
> transparent_hugepage_adjust is not very pretty, but this is also how
> it's solved on x86 and seems to be simply an artifact on how THPs
> behave. This should eventually be shared across architectures if
> possible, but that can always be changed down the road.
>
> Signed-off-by: Christoffer Dall <[email protected]>
>
> ---
> Changelog[v2]:
> - THP handling moved into separate patch.
> - Minor changes and clarified comment in transparent_hugepage_adjust
> from Marc Z's review.
> ---
> arch/arm/kvm/mmu.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index cab031b..0a856a0 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -42,7 +42,7 @@ static unsigned long hyp_idmap_start;
> static unsigned long hyp_idmap_end;
> static phys_addr_t hyp_idmap_vector;
>
> -#define kvm_pmd_huge(_x) (pmd_huge(_x))
> +#define kvm_pmd_huge(_x) (pmd_huge(_x) || pmd_trans_huge(_x))
>
> static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> {
> @@ -576,6 +576,47 @@ out:
> return ret;
> }
>
> +static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
> +{
> + pfn_t pfn = *pfnp;
> + gfn_t gfn = *ipap >> PAGE_SHIFT;
> +
> + if (PageTransCompound(pfn_to_page(pfn))) {
> + unsigned long mask;
> + /*
> + * The address we faulted on is backed by a transparent huge
> + * page. However, because we map the compound huge page and
> + * not the individual tail page, we need to transfer the
> + * refcount to the head page. We have to be careful that the
> + * THP doesn't start to split while we are adjusting the
> + * refcounts.
> + *
> + * We are sure this doesn't happen, because mmu_notifier_retry
> + * was succesful and we are holding the mmu_lock, so if this
successful
> + * THP is trying to split, it will be blocked in the mmu
> + * notifier before touching any of the pages, specifically
> + * before being able to call __split_huge_page_refcount().
> + *
> + * We can therefore safely transfer the refcount from PG_tail
> + * to PG_head and switch the pfn from a tail page to the head
> + * page accordingly.
> + */
> + mask = PTRS_PER_PMD - 1;
> + VM_BUG_ON((gfn & mask) != (pfn & mask));
> + if (pfn & mask) {
> + *ipap &= PMD_MASK;
> + kvm_release_pfn_clean(pfn);
> + pfn &= ~mask;
> + kvm_get_pfn(pfn);
> + *pfnp = pfn;
> + }
> +
> + return true;
> + }
> +
> + return false;
> +}
> +
> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> struct kvm_memory_slot *memslot,
> unsigned long fault_status)
> @@ -632,6 +673,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu,
> phys_addr_t fault_ipa,
> spin_lock(&kvm->mmu_lock);
> if (mmu_notifier_retry(kvm, mmu_seq))
> goto out_unlock;
> + if (!hugetlb && !force_pte)
> + hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
>
> if (hugetlb) {
> pmd_t new_pmd = pfn_pmd(pfn, PAGE_S2);
>
Looks good. I think that if you fix the minor issues I have with the
previous patch, this is good to go.
M.
--
Jazz is not dead. It just smells funny...
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