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SubjectRe: [PATCH v4 4/7] KVM: arm64: Support PUD hugepage in stage2_is_exec()
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Hi Punit,

On 05/07/18 15:08, 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 | 10 +++++++++-
> 4 files changed, 22 insertions(+), 1 deletion(-)
>
> 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] */
> +

The changes above look good to me. Please see below.

> /*
> * Memory Attribute override for Stage-2 (MemAttr[3:0])
> */
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index db04b18218c1..ccdea0edabb3 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -1040,10 +1040,18 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
>
> static bool stage2_is_exec(struct kvm *kvm, phys_addr_t addr)
> {
> + pud_t *pudp;
> pmd_t *pmdp;
> pte_t *ptep;
>
> - 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))
> + return kvm_s2pud_exec(pudp);
> +
> + pmdp = stage2_pmd_offset(pudp, addr);
> if (!pmdp || pmd_none(*pmdp) || !pmd_present(*pmdp))
> return false;

I am wondering if we need a slightly better way to deal with this
kind of operation. We seem to duplicate the above operation (here and
in the following patches), i.e, finding the "leaf entry" for a given
address and follow the checks one level up at a time.

So instead of doing, stage2_get_pud() and walking down everywhere this
is needed, how about adding :

/* Returns true if the leaf entry is found and updates the relevant pointer */
found = stage2_get_leaf_entry(kvm, NULL, addr, &pudp, &pmdp, &ptep)

which could set the appropriate entry and we could check the result here.

Cheers
Suzuki

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