Re: [PATCH v5 6/6] arm64: KVM: Implement 4 levels of translation tables for HYP and stage2

From: Christoffer Dall
Date: Tue May 06 2014 - 06:49:32 EST

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On Thu, May 01, 2014 at 11:34:19AM +0900, Jungseok Lee wrote:
> This patch adds 4 levels of translation tables implementation for both
> HYP and stage2.
>
> Both symmetric and asymmetric configurations for page size and translation
> levels are are validated on Fast Models:
>
> 1) 4KB + 3 levels guest on 4KB + 3 levels host
>
> 2) 4KB + 4 levels guest on 4KB + 3 levels host
>
> 3) 64KB + 2 levels guest on 4KB + 3 levels host
>
> 4) 4KB + 3 levels guest on 4KB + 4 levels host
>
> 5) 4KB + 4 levels guest on 4KB + 4 levels host
>
> 6) 64KB + 2 levels guest on 4KB + 4 levels host
>
> 7) 4KB + 3 levels guest on 64KB + 2 levels host
>
> 8) 4KB + 4 levels guest on 64KB + 2 levels host
>
> 9) 64KB + 2 levels guest on 64KB + 2 levels host
>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> Signed-off-by: Jungseok Lee <jays.lee@xxxxxxxxxxx>
> Reviewed-by: Sungjinn Chung <sungjinn.chung@xxxxxxxxxxx>
> ---
> arch/arm/include/asm/kvm_mmu.h | 10 +++++
> arch/arm/kvm/mmu.c | 88 +++++++++++++++++++++++++++++++++-----
> arch/arm64/include/asm/kvm_arm.h | 34 ++++++++++++---
> arch/arm64/include/asm/kvm_mmu.h | 12 ++++++
> 4 files changed, 127 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 5c7aa3c..31eaaa6 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -37,6 +37,11 @@
> */
> #define TRAMPOLINE_VA UL(CONFIG_VECTORS_BASE)
>
> +/*
> + * MMU_CACHE_MIN_PAGES is the number of stage2 page table translation levels.
> + */
> +#define MMU_CACHE_MIN_PAGES 2
> +

I would prefer this was KVM_MMU_CACHE_MIN_PAGES

> #ifndef __ASSEMBLY__
>
> #include <asm/cacheflush.h>
> @@ -94,6 +99,11 @@ static inline void kvm_clean_pgd(pgd_t *pgd)
> clean_dcache_area(pgd, PTRS_PER_S2_PGD * sizeof(pgd_t));
> }
>
> +static inline void kvm_clean_pmd(pmd_t *pmd)
> +{
> + clean_dcache_area(pmd, PTRS_PER_PMD * sizeof(pmd_t));
> +}
> +
> static inline void kvm_clean_pmd_entry(pmd_t *pmd)
> {
> clean_pmd_entry(pmd);
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 80bb1e6..3ffbdfb 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -388,13 +388,44 @@ static int create_hyp_pmd_mappings(pud_t *pud, unsigned long start,
> return 0;
> }
>
> +static int create_hyp_pud_mappings(pgd_t *pgd, unsigned long start,
> + unsigned long end, unsigned long pfn,
> + pgprot_t prot)
> +{
> + pud_t *pud;
> + pmd_t *pmd;
> + unsigned long addr, next;
> +
> + addr = start;
> + do {
> + pud = pud_offset(pgd, addr);
> +
> + if (pud_none_or_clear_bad(pud)) {
> + pmd = pmd_alloc_one(NULL, addr);
> + if (!pmd) {
> + kvm_err("Cannot allocate Hyp pmd\n");
> + return -ENOMEM;
> + }
> + pud_populate(NULL, pud, pmd);
> + get_page(virt_to_page(pud));
> + kvm_flush_dcache_to_poc(pud, sizeof(*pud));
> + }
> +
> + next = pud_addr_end(addr, end);
> +
> + create_hyp_pmd_mappings(pud, addr, next, pfn, prot);
> + pfn += (next - addr) >> PAGE_SHIFT;
> + } while (addr = next, addr != end);
> +
> + return 0;
> +}
> +
> static int __create_hyp_mappings(pgd_t *pgdp,
> unsigned long start, unsigned long end,
> unsigned long pfn, pgprot_t prot)
> {
> pgd_t *pgd;
> pud_t *pud;
> - pmd_t *pmd;
> unsigned long addr, next;
> int err = 0;
>
> @@ -403,22 +434,23 @@ static int __create_hyp_mappings(pgd_t *pgdp,
> end = PAGE_ALIGN(end);
> do {
> pgd = pgdp + pgd_index(addr);
> - pud = pud_offset(pgd, addr);
>
> - if (pud_none_or_clear_bad(pud)) {
> - pmd = pmd_alloc_one(NULL, addr);
> - if (!pmd) {
> - kvm_err("Cannot allocate Hyp pmd\n");
> + if (pgd_none(*pgd)) {
> + pud = pud_alloc_one(NULL, addr);
> + if (!pud) {
> + kvm_err("Cannot allocate Hyp pud\n");
> err = -ENOMEM;
> goto out;
> }
> - pud_populate(NULL, pud, pmd);
> - get_page(virt_to_page(pud));
> - kvm_flush_dcache_to_poc(pud, sizeof(*pud));
> + pgd_populate(NULL, pgd, pud);
> + get_page(virt_to_page(pgd));
> + kvm_flush_dcache_to_poc(pgd, sizeof(*pgd));
> }
>
> next = pgd_addr_end(addr, end);
> - err = create_hyp_pmd_mappings(pud, addr, next, pfn, prot);
> +
> + err = create_hyp_pud_mappings(pgd, addr, next, pfn, prot);
> +

super nit: this whitespacing looks weird

> if (err)
> goto out;
> pfn += (next - addr) >> PAGE_SHIFT;
> @@ -563,6 +595,24 @@ void kvm_free_stage2_pgd(struct kvm *kvm)
> kvm->arch.pgd = NULL;
> }
>
> +static pud_t *stage2_get_pud(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> + phys_addr_t addr)
> +{
> + pgd_t *pgd;
> + pud_t *pud;
> +
> + pgd = kvm->arch.pgd + pgd_index(addr);
> + if (pgd_none(*pgd)) {
> + if (!cache)
> + return NULL;
> + pud = mmu_memory_cache_alloc(cache);
> + pgd_populate(NULL, pgd, pud);
> + get_page(virt_to_page(pgd));
> + }
> +
> + return pud_offset(pgd, addr);
> +}
> +
> static pmd_t *stage2_get_pmd(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> phys_addr_t addr)
> {
> @@ -614,9 +664,24 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
> static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> phys_addr_t addr, const pte_t *new_pte, bool iomap)
> {
> + pud_t *pud;
> pmd_t *pmd;
> pte_t *pte, old_pte;
>
> + /* Create stage-2 page table mapping - Level 0 */
> + pud = stage2_get_pud(kvm, cache, addr);
> + if (!pud)
> + return 0;
> +
> + if (pud_none(*pud)) {
> + if (!cache)
> + return 0;
> + pmd = mmu_memory_cache_alloc(cache);
> + kvm_clean_pmd(pmd);
> + pud_populate(NULL, pud, pmd);
> + get_page(virt_to_page(pud));
> + }
> +

Now we are doing this work twice, here and in stage2_get_pmd. Can you
not simply call stage2_get_pmd() from stage2_get_pud() and get rid of
this code?

> /* Create stage-2 page table mapping - Level 1 */
> pmd = stage2_get_pmd(kvm, cache, addr);
> if (!pmd) {
> @@ -675,7 +740,8 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> for (addr = guest_ipa; addr < end; addr += PAGE_SIZE) {
> pte_t pte = pfn_pte(pfn, PAGE_S2_DEVICE);
>
> - ret = mmu_topup_memory_cache(&cache, 2, 2);
> + ret = mmu_topup_memory_cache(&cache, MMU_CACHE_MIN_PAGES,
> + MMU_CACHE_MIN_PAGES);
> if (ret)
> goto out;
> spin_lock(&kvm->mmu_lock);
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index 3d69030..29c9c25 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -117,9 +117,10 @@
> #define VTCR_EL2_IRGN0_MASK (3 << 8)
> #define VTCR_EL2_IRGN0_WBWA (1 << 8)
> #define VTCR_EL2_SL0_MASK (3 << 6)
> +#define VTCR_EL2_SL0_LVL0 (2 << 6)
> #define VTCR_EL2_SL0_LVL1 (1 << 6)
> #define VTCR_EL2_T0SZ_MASK 0x3f
> -#define VTCR_EL2_T0SZ_40B 24
> +#define VTCR_EL2_T0SZ(bits) (64 - (bits))
>
> #ifdef CONFIG_ARM64_64K_PAGES
> /*
> @@ -129,11 +130,14 @@
> * 64kB pages (TG0 = 1)
> * 2 level page tables (SL = 1)
> */
> +#define VTTBR_OUTPUT_BITS 40

This is confusing, because the PS field is populated at runtime in
arch/arm64/kvm/hyp-init.S and depends on the PARange field in
ID_AA64MMFR0_EL1.

So the existing code actually looks wrong to me in that we will generate
a Stage-2 translation fault for all IPAs > 2^40 on systems with >40 bits
physical address space. (Which will also be the case after this patch).

> #define VTCR_EL2_FLAGS (VTCR_EL2_TG0_64K | VTCR_EL2_SH0_INNER | \
> VTCR_EL2_ORGN0_WBWA | VTCR_EL2_IRGN0_WBWA | \
> - VTCR_EL2_SL0_LVL1 | VTCR_EL2_T0SZ_40B)
> -#define VTTBR_X (38 - VTCR_EL2_T0SZ_40B)
> + VTCR_EL2_SL0_LVL1 | \
> + VTCR_EL2_T0SZ(VTTBR_OUTPUT_BITS))
> +#define VTTBR_X (38 - VTCR_EL2_T0SZ(VTTBR_OUTPUT_BITS))

I spent hours trying to remember how to make sense of these hard-coded
numbers, and failed.

Now when you're adding yet another one, please add an explanation on how
to decode the VTTBR_X and why it all adds up as it should.

> #else
> +#ifndef CONFIG_ARM64_4_LEVELS
> /*
> * Stage2 translation configuration:
> * 40bits output (PS = 2)
> @@ -141,14 +145,32 @@
> * 4kB pages (TG0 = 0)
> * 3 level page tables (SL = 1)
> */
> +#define VTTBR_OUTPUT_BITS 40
> #define VTCR_EL2_FLAGS (VTCR_EL2_TG0_4K | VTCR_EL2_SH0_INNER | \
> VTCR_EL2_ORGN0_WBWA | VTCR_EL2_IRGN0_WBWA | \
> - VTCR_EL2_SL0_LVL1 | VTCR_EL2_T0SZ_40B)
> -#define VTTBR_X (37 - VTCR_EL2_T0SZ_40B)
> + VTCR_EL2_SL0_LVL1 | \
> + VTCR_EL2_T0SZ(VTTBR_OUTPUT_BITS))
> +#define VTTBR_X (37 - VTCR_EL2_T0SZ(VTTBR_OUTPUT_BITS))
> +#else
> +/*
> + * Stage2 translation configuration:
> + * 40bits output (PS = 2)
> + * 48bits input (T0SZ = 16)
> + * 4kB pages (TG0 = 0)
> + * 4 level page tables (SL = 2)
> + */
> +#define VTTBR_OUTPUT_BITS 48

You're defining output bits to 48, but your comment says 40 bits output,
and 48 bits input here.

I suspect the problem here in general is that the T0SZ field size
regulates the size of the input to the Stage-2 translation, and not the
output, and therefore that your comment is correct (except that PS will
not be fixed to 2), and that the input will indeed be 48 bits.

> +#define VTCR_EL2_FLAGS (VTCR_EL2_TG0_4K | VTCR_EL2_SH0_INNER | \
> + VTCR_EL2_ORGN0_WBWA | VTCR_EL2_IRGN0_WBWA | \
> + VTCR_EL2_SL0_LVL0 | \
> + VTCR_EL2_T0SZ(VTTBR_OUTPUT_BITS))
> +#define VTTBR_X (29 - VTCR_EL2_T0SZ(VTTBR_OUTPUT_BITS))

Definitely need to key so I can verify that 29 is correct or a comment
with a direct reference to the arch. document stating that this is the
correct formula.

> +#endif
> #endif
>
> #define VTTBR_BADDR_SHIFT (VTTBR_X - 1)
> -#define VTTBR_BADDR_MASK (((1LLU << (40 - VTTBR_X)) - 1) << VTTBR_BADDR_SHIFT)
> +#define VTTBR_BADDR_SIZE (1LLU << (VTTBR_OUTPUT_BITS - VTTBR_X))
> +#define VTTBR_BADDR_MASK ((VTTBR_BADDR_SIZE - 1) << VTTBR_BADDR_SHIFT)
> #define VTTBR_VMID_SHIFT (48LLU)
> #define VTTBR_VMID_MASK (0xffLLU << VTTBR_VMID_SHIFT)
>
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 7d29847..72bf9ab 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -41,6 +41,17 @@
> */
> #define TRAMPOLINE_VA (HYP_PAGE_OFFSET_MASK & PAGE_MASK)
>
> +/*
> + * MMU_CACHE_MIN_PAGES is the number of stage2 page table translation levels.
> + */
> +#ifdef CONFIG_ARM64_2_LEVELS
> +#define MMU_CACHE_MIN_PAGES 1
> +#elif defined(CONFIG_ARM64_3_LEVELS)
> +#define MMU_CACHE_MIN_PAGES 2
> +#else
> +#define MMU_CACHE_MIN_PAGES 3
> +#endif
> +
> #ifdef __ASSEMBLY__
>
> /*
> @@ -107,6 +118,7 @@ static inline bool kvm_is_write_fault(unsigned long esr)
> }
>
> static inline void kvm_clean_pgd(pgd_t *pgd) {}
> +static inline void kvm_clean_pmd(pmd_t *pmd) {}
> static inline void kvm_clean_pmd_entry(pmd_t *pmd) {}
> static inline void kvm_clean_pte(pte_t *pte) {}
> static inline void kvm_clean_pte_entry(pte_t *pte) {}
> --
> 1.7.10.4
>
>

Thanks,
-Christoffer
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