Re: [RFC 4/4] KVM: arm64: Add support for PUD hugepages at stage 2

Christoffer Dall
2018-02-06T14:55:14Z

On Wed, Jan 10, 2018 at 07:07:29PM +0000, Punit Agrawal wrote:
> KVM only supports PMD hugepages at stage 2. Extend the stage 2 fault
> handling to add support for PUD hugepages.
>
> Addition of PUD hugpage support enables additional hugepage sizes (1G

*hugepage

> with 4K granule and 4TB with 64k granule) which can be useful on cores
> that have support for mapping larger block sizes in the TLB entries.
>
> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Christoffer Dall <christoffer.dall@linaro.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> ---
> arch/arm/include/asm/kvm_mmu.h | 10 +++++
> arch/arm/include/asm/pgtable-3level.h | 2 +
> arch/arm64/include/asm/kvm_mmu.h | 19 +++++++++
> arch/arm64/include/asm/pgtable-hwdef.h | 2 +
> arch/arm64/include/asm/pgtable.h | 4 ++
> virt/kvm/arm/mmu.c | 72 +++++++++++++++++++++++++++++-----
> 6 files changed, 99 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 3fbe919b9181..6e2e34348cb3 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -59,6 +59,10 @@ phys_addr_t kvm_get_idmap_vector(void);
> int kvm_mmu_init(void);
> void kvm_clear_hyp_idmap(void);
>
> +static inline void kvm_set_pud(pud_t *pud, pud_t new_pud)
> +{
> +}
> +
> static inline void kvm_set_pmd(pmd_t *pmd, pmd_t new_pmd)
> {
> *pmd = new_pmd;
> @@ -230,6 +234,12 @@ static inline unsigned int kvm_get_vmid_bits(void)
> return 8;
> }
>
> +static inline pud_t stage2_build_pud(kvm_pfn_t pfn, pgprot_t mem_type,
> + bool writable)
> +{
> + return __pud(0);
> +}
> +
> #endif /* !__ASSEMBLY__ */
>
> #endif /* __ARM_KVM_MMU_H__ */
> diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
> index 1a7a17b2a1ba..97e04fdbfa85 100644
> --- a/arch/arm/include/asm/pgtable-3level.h
> +++ b/arch/arm/include/asm/pgtable-3level.h
> @@ -249,6 +249,8 @@ PMD_BIT_FUNC(mkyoung, |= PMD_SECT_AF);
> #define pfn_pmd(pfn,prot) (__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
> #define mk_pmd(page,prot) pfn_pmd(page_to_pfn(page),prot)
>
> +#define pud_pfn(pud) (((pud_val(pud) & PUD_MASK) & PHYS_MASK) >> PAGE_SHIFT)
> +

does this make sense on 32-bit arm? Is this ever going to get called
and return something meaningful in that case?

> /* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
> static inline pmd_t pmd_mknotpresent(pmd_t pmd)
> {
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index dbfd18e08cfb..89eac3dbe123 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -160,6 +160,7 @@ void kvm_clear_hyp_idmap(void);
>
> #define kvm_set_pte(ptep, pte) set_pte(ptep, pte)
> #define kvm_set_pmd(pmdp, pmd) set_pmd(pmdp, pmd)
> +#define kvm_set_pud(pudp, pud) set_pud(pudp, pud)
>
> static inline pte_t kvm_s2pte_mkwrite(pte_t pte)
> {
> @@ -173,6 +174,12 @@ static inline pmd_t kvm_s2pmd_mkwrite(pmd_t pmd)
> return pmd;
> }
>
> +static inline pud_t kvm_s2pud_mkwrite(pud_t pud)
> +{
> + pud_val(pud) |= PUD_S2_RDWR;
> + return pud;
> +}
> +
> static inline void kvm_set_s2pte_readonly(pte_t *pte)
> {
> pteval_t old_pteval, pteval;
> @@ -319,5 +326,17 @@ static inline unsigned int kvm_get_vmid_bits(void)
> return (cpuid_feature_extract_unsigned_field(reg, ID_AA64MMFR1_VMIDBITS_SHIFT) == 2) ? 16 : 8;
> }
>
> +static inline pud_t stage2_build_pud(kvm_pfn_t pfn, pgprot_t mem_type,
> + bool writable)
> +{
> + pud_t pud = pfn_pud(pfn, mem_type);
> +
> + pud = pud_mkhuge(pud);
> + if (writable)
> + pud = kvm_s2pud_mkwrite(pud);
> +
> + return pud;
> +}
> +
> #endif /* __ASSEMBLY__ */
> #endif /* __ARM64_KVM_MMU_H__ */
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index 40a998cdd399..a091a6192eee 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -181,6 +181,8 @@
> #define PMD_S2_RDONLY (_AT(pmdval_t, 1) << 6) /* HAP[2:1] */
> #define PMD_S2_RDWR (_AT(pmdval_t, 3) << 6) /* HAP[2:1] */
>
> +#define PUD_S2_RDWR (_AT(pudval_t, 3) << 6) /* HAP[2:1] */
> +
> /*
> * Memory Attribute override for Stage-2 (MemAttr[3:0])
> */
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index bdcc7f1c9d06..d5ffff4369d2 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -362,7 +362,11 @@ static inline int pmd_protnone(pmd_t pmd)
> #define mk_pmd(page,prot) pfn_pmd(page_to_pfn(page),prot)
>
> #define pud_write(pud) pte_write(pud_pte(pud))
> +
> +#define pud_mkhuge(pud) (__pud(pud_val(pud) & ~PUD_TABLE_BIT))
> +
> #define pud_pfn(pud) (((pud_val(pud) & PUD_MASK) & PHYS_MASK) >> PAGE_SHIFT)
> +#define pfn_pud(pfn, prot) (__pud(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
>
> #define set_pmd_at(mm, addr, pmdp, pmd) set_pte_at(mm, addr, (pte_t *)pmdp, pmd_pte(pmd))
>
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index f02219a91b19..5362de098768 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -872,6 +872,32 @@ static pud_t *stage2_get_pud(struct kvm *kvm, struct kvm_mmu_memory_cache *cache
> return stage2_pud_offset(pgd, addr);
> }
>
> +static int stage2_set_pud_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
> + *cache, phys_addr_t addr, const pud_t *new_pud)
> +{
> + pud_t *pud, old_pud;
> +
> + pud = stage2_get_pud(kvm, cache, addr);
> + VM_BUG_ON(!pud);
> +
> + /*
> + * Mapping in huge pages should only happen through a fault.
> + */
> + VM_BUG_ON(stage2_pud_present(*pud) &&
> + pud_pfn(*pud) != pud_pfn(*new_pud));
> +
> + old_pud = *pud;
> + if (stage2_pud_present(old_pud)) {
> + stage2_pud_clear(pud);
> + kvm_tlb_flush_vmid_ipa(kvm, addr);
> + } else {
> + get_page(virt_to_page(pud));
> + }
> +
> + kvm_set_pud(pud, *new_pud);
> + return 0;
> +}
> +
> static pmd_t *stage2_get_pmd(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> phys_addr_t addr)
> {
> @@ -1307,6 +1333,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> kvm_pfn_t pfn;
> pgprot_t mem_type = PAGE_S2;
> bool logging_active = memslot_is_logging(memslot);
> + unsigned long vma_pagesize;
> unsigned long flags = 0;
>
> write_fault = kvm_is_write_fault(vcpu);
> @@ -1324,9 +1351,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
> }
>
> - if (vma_kernel_pagesize(vma) == PMD_SIZE && !logging_active) {
> + vma_pagesize = vma_kernel_pagesize(vma);
> + if ((vma_pagesize == PMD_SIZE || vma_pagesize == PUD_SIZE) &&
> + !logging_active) {
> + struct hstate *h = hstate_vma(vma);
> +
> hugetlb = true;
> - gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
> + gfn = (fault_ipa & huge_page_mask(h)) >> PAGE_SHIFT;
> } else {
> /*
> * Pages belonging to memslots that don't have the same
> @@ -1393,17 +1424,38 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (mmu_notifier_retry(kvm, mmu_seq))
> goto out_unlock;
>
> - if (!hugetlb && !force_pte)
> + if (!hugetlb && !force_pte) {
> + /*
> + * We only support PMD_SIZE transparent
> + * hugepages. This code will need updates if we enable
> + * other page sizes for THP.
> + */
> hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
> + vma_pagesize = PMD_SIZE;
> + }
>
> if (hugetlb) {
> - pmd_t new_pmd = stage2_build_pmd(pfn, mem_type, writable);
> -
> - if (writable)
> - kvm_set_pfn_dirty(pfn);
> -
> - coherent_cache_guest_page(vcpu, pfn, PMD_SIZE);
> - ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
> + if (vma_pagesize == PUD_SIZE) {
> + pud_t new_pud;
> +
> + new_pud = stage2_build_pud(pfn, mem_type, writable);
> + if (writable)
> + kvm_set_pfn_dirty(pfn);
> +
> + coherent_cache_guest_page(vcpu, pfn, PUD_SIZE);
> + ret = stage2_set_pud_huge(kvm, memcache,
> + fault_ipa, &new_pud);
> + } else {
> + pmd_t new_pmd;
> +
> + new_pmd = stage2_build_pmd(pfn, mem_type, writable);
> + if (writable)
> + kvm_set_pfn_dirty(pfn);
> +
> + coherent_cache_guest_page(vcpu, pfn, PMD_SIZE);
> + ret = stage2_set_pmd_huge(kvm, memcache,
> + fault_ipa, &new_pmd);
> + }

This stuff needs rebasing onto v4.16-rc1 when we get there, and it will
clash with Marc's icache optimizations.

But, you should be able to move kvm_set_pfn_dirty() out of the
size-conditional section and also call the cache maintenance functions
using vma_pagesize as parameter.

> } else {
> pte_t new_pte = pfn_pte(pfn, mem_type);
>
> --
> 2.15.1
>

Thanks,
-Christoffer