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SubjectRe: [PATCH v5 4/7] KVM: arm64: Support PUD hugepage in stage2_is_exec()
Date
Suzuki K Poulose <Suzuki.Poulose@arm.com> writes:

> On 09/07/18 15:41, Punit Agrawal wrote:
>> In preparation for creating PUD hugepages at stage 2, add support for
>> detecting execute permissions on PUD page table entries. Faults due to
>> lack of execute permissions on page table entries is used to perform
>> i-cache invalidation on first execute.
>>
>> Provide trivial implementations of arm32 helpers to allow sharing of
>> code.
>>
>> Signed-off-by: Punit Agrawal <punit.agrawal@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 | 6 ++++
>> arch/arm64/include/asm/kvm_mmu.h | 5 +++
>> arch/arm64/include/asm/pgtable-hwdef.h | 2 ++
>> virt/kvm/arm/mmu.c | 49 +++++++++++++++++++++++---
>> 4 files changed, 57 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
>> index c23722f75d5c..d05c8986e495 100644
>> --- a/arch/arm/include/asm/kvm_mmu.h
>> +++ b/arch/arm/include/asm/kvm_mmu.h
>> @@ -96,6 +96,12 @@ static inline bool kvm_s2pud_readonly(pud_t *pud)
>> }
>> +static inline bool kvm_s2pud_exec(pud_t *pud)
>> +{
>> + BUG();
>> + return false;
>> +}
>> +
>> static inline void kvm_set_pmd(pmd_t *pmd, pmd_t new_pmd)
>> {
>> *pmd = new_pmd;
>> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
>> index 84051930ddfe..15bc1be8f82f 100644
>> --- a/arch/arm64/include/asm/kvm_mmu.h
>> +++ b/arch/arm64/include/asm/kvm_mmu.h
>> @@ -249,6 +249,11 @@ static inline bool kvm_s2pud_readonly(pud_t *pudp)
>> return kvm_s2pte_readonly((pte_t *)pudp);
>> }
>> +static inline bool kvm_s2pud_exec(pud_t *pudp)
>> +{
>> + return !(READ_ONCE(pud_val(*pudp)) & PUD_S2_XN);
>> +}
>> +
>> static inline bool kvm_page_empty(void *ptr)
>> {
>> struct page *ptr_page = virt_to_page(ptr);
>> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
>> index fd208eac9f2a..10ae592b78b8 100644
>> --- a/arch/arm64/include/asm/pgtable-hwdef.h
>> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
>> @@ -193,6 +193,8 @@
>> #define PMD_S2_RDWR (_AT(pmdval_t, 3) << 6) /* HAP[2:1] */
>> #define PMD_S2_XN (_AT(pmdval_t, 2) << 53) /* XN[1:0] */
>> +#define PUD_S2_XN (_AT(pudval_t, 2) << 53) /* XN[1:0]
>> */
>> +
>> /*
>> * Memory Attribute override for Stage-2 (MemAttr[3:0])
>> */
>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>> index ed8f8271c389..e73909a31e02 100644
>> --- a/virt/kvm/arm/mmu.c
>> +++ b/virt/kvm/arm/mmu.c
>> @@ -1038,23 +1038,62 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
>> return 0;
>> }
>> -static bool stage2_is_exec(struct kvm *kvm, phys_addr_t addr)
>> +/*
>> + * stage2_get_leaf_entry - walk the stage2 VM page tables and return
>> + * true if a valid and present leaf-entry is found. A pointer to the
>> + * leaf-entry is returned in the appropriate level variable - pudpp,
>> + * pmdpp, ptepp.
>> + */
>> +static bool stage2_get_leaf_entry(struct kvm *kvm, phys_addr_t addr,
>> + pud_t **pudpp, pmd_t **pmdpp, pte_t **ptepp)
>> {
>> + pud_t *pudp;
>> pmd_t *pmdp;
>> pte_t *ptep;
>
> nit: As mentioned in the other thread, you may initialize the reference
> pointers to NULL to make sure we start clean and avoid the initialization
> everywhere this is called.

I took the approach to not touch the pointers unless they are being
assigned a valid pointer. I'll initialise the incoming pointers (p*dpp)
before proceeding with the table walk.

Thanks,
Punit

>
>> - pmdp = stage2_get_pmd(kvm, NULL, addr);
>> + pudp = stage2_get_pud(kvm, NULL, addr);
>> + if (!pudp || pud_none(*pudp) || !pud_present(*pudp))
>> + return false;
>> +
>> + if (pud_huge(*pudp)) {
>> + *pudpp = pudp;
>> + return true;
>> + }
>> +
>> + pmdp = stage2_pmd_offset(pudp, addr);
>> if (!pmdp || pmd_none(*pmdp) || !pmd_present(*pmdp))
>> return false;
>> - if (pmd_thp_or_huge(*pmdp))
>> - return kvm_s2pmd_exec(pmdp);
>> + if (pmd_thp_or_huge(*pmdp)) {
>> + *pmdpp = pmdp;
>> + return true;
>> + }
>> ptep = pte_offset_kernel(pmdp, addr);
>> if (!ptep || pte_none(*ptep) || !pte_present(*ptep))
>> return false;
>> - return kvm_s2pte_exec(ptep);
>> + *ptepp = ptep;
>> + return true;
>> +}
>> +
>> +static bool stage2_is_exec(struct kvm *kvm, phys_addr_t addr)
>> +{
>> + pud_t *pudp = NULL;
>> + pmd_t *pmdp = NULL;
>> + pte_t *ptep = NULL;
>> + bool found;
>> +
>> + found = stage2_get_leaf_entry(kvm, addr, &pudp, &pmdp, &ptep);
>> + if (!found)
>> + return false;
>> +
>> + if (pudp)
>> + return kvm_s2pud_exec(pudp);
>> + else if (pmdp)
>> + return kvm_s2pmd_exec(pmdp);
>> + else
>> + return kvm_s2pte_exec(ptep);
>> }
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> _______________________________________________
> kvmarm mailing list
> kvmarm@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
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