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SubjectRe: [PATCH v9 6/8] KVM: arm64: Support handling access faults for PUD hugepages
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On 10/31/2018 11:27 PM, Punit Agrawal wrote:
> In preparation for creating larger hugepages at Stage 2, extend the
> access fault handling at Stage 2 to support PUD hugepages when
> encountered.
>
> Provide trivial helpers for arm32 to allow sharing of code.
>
> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Christoffer Dall <christoffer.dall@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---
> arch/arm/include/asm/kvm_mmu.h | 9 +++++++++
> arch/arm64/include/asm/kvm_mmu.h | 7 +++++++
> arch/arm64/include/asm/pgtable.h | 6 ++++++
> virt/kvm/arm/mmu.c | 22 +++++++++++-----------
> 4 files changed, 33 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 839a619873d3..fea5e723e3ac 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -85,6 +85,9 @@ void kvm_clear_hyp_idmap(void);
> #define kvm_pfn_pte(pfn, prot) pfn_pte(pfn, prot)
> #define kvm_pfn_pmd(pfn, prot) pfn_pmd(pfn, prot)
>
> +#define kvm_pud_pfn(pud) ({ BUG(); 0; })
> +
> +
> #define kvm_pmd_mkhuge(pmd) pmd_mkhuge(pmd)
>
> /*
> @@ -108,6 +111,12 @@ static inline bool kvm_s2pud_exec(pud_t *pud)
> return false;
> }
>
> +static inline pud_t kvm_s2pud_mkyoung(pud_t pud)
> +{
> + BUG();
> + return pud;
> +}
> +
> static inline pte_t kvm_s2pte_mkwrite(pte_t pte)
> {
> pte_val(pte) |= L_PTE_S2_RDWR;
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index c755b37b3f92..612032bbb428 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -187,6 +187,8 @@ void kvm_clear_hyp_idmap(void);
> #define kvm_pfn_pte(pfn, prot) pfn_pte(pfn, prot)
> #define kvm_pfn_pmd(pfn, prot) pfn_pmd(pfn, prot)
>
> +#define kvm_pud_pfn(pud) pud_pfn(pud)
> +
> #define kvm_pmd_mkhuge(pmd) pmd_mkhuge(pmd)
>
> static inline pte_t kvm_s2pte_mkwrite(pte_t pte)
> @@ -266,6 +268,11 @@ static inline bool kvm_s2pud_exec(pud_t *pudp)
> return !(READ_ONCE(pud_val(*pudp)) & PUD_S2_XN);
> }
>
> +static inline pud_t kvm_s2pud_mkyoung(pud_t pud)
> +{
> + return pud_mkyoung(pud);
> +}
> +
> #define hyp_pte_table_empty(ptep) kvm_page_empty(ptep)
>
> #ifdef __PAGETABLE_PMD_FOLDED
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 50b1ef8584c0..f51e2271e6a3 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -314,6 +314,11 @@ static inline pte_t pud_pte(pud_t pud)
> return __pte(pud_val(pud));
> }
>
> +static inline pud_t pte_pud(pte_t pte)
> +{
> + return __pud(pte_val(pte));
> +}
> +

Yeah these would be required for PUD based THP when enabled.

> static inline pmd_t pud_pmd(pud_t pud)
> {
> return __pmd(pud_val(pud));
> @@ -381,6 +386,7 @@ static inline int pmd_protnone(pmd_t pmd)
> #define pfn_pmd(pfn,prot) __pmd(__phys_to_pmd_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot))
> #define mk_pmd(page,prot) pfn_pmd(page_to_pfn(page),prot)
>
> +#define pud_mkyoung(pud) pte_pud(pte_mkyoung(pud_pte(pud)))
> #define pud_write(pud) pte_write(pud_pte(pud))
>
> #define __pud_to_phys(pud) __pte_to_phys(pud_pte(pud))
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 8e44dccd1b47..bd749601195f 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -1698,6 +1698,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> */
> static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
> {
> + pud_t *pud;
> pmd_t *pmd;
> pte_t *pte;
> kvm_pfn_t pfn;
> @@ -1707,24 +1708,23 @@ static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
>
> spin_lock(&vcpu->kvm->mmu_lock);
>
> - pmd = stage2_get_pmd(vcpu->kvm, NULL, fault_ipa);
> - if (!pmd || pmd_none(*pmd)) /* Nothing there */
> + if (!stage2_get_leaf_entry(vcpu->kvm, fault_ipa, &pud, &pmd, &pte))
> goto out;
>
> - if (pmd_thp_or_huge(*pmd)) { /* THP, HugeTLB */
> + if (pud) { /* HugeTLB */
> + *pud = kvm_s2pud_mkyoung(*pud);
> + pfn = kvm_pud_pfn(*pud);
> + pfn_valid = true;
> + } else if (pmd) { /* THP, HugeTLB */
> *pmd = pmd_mkyoung(*pmd);
> pfn = pmd_pfn(*pmd);
> pfn_valid = true;
> - goto out;
> + } else {
> + *pte = pte_mkyoung(*pte); /* Just a page... */
> + pfn = pte_pfn(*pte);
> + pfn_valid = true;
> }

As mentioned before stage2_get_leaf_entry() is not required for the previous
patch and handle_access_fault() can definitely do without it. The existing
page table walker flow is better than this helper which takes like three
different arguments and makes semantics more complicated than required.

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