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

[Christoffer Dall]

On Fri, Apr 20, 2018 at 03:54:09PM +0100, 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 hugepage support enables additional hugepage
> sizes (e.g., 1G with 4K granule) which can be useful on cores that
> support mapping larger block sizes in the TLB entries.
> 
> Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
> Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> ---
>  arch/arm/include/asm/kvm_mmu.h         | 19 +++++++++
>  arch/arm64/include/asm/kvm_mmu.h       | 15 +++++++
>  arch/arm64/include/asm/pgtable-hwdef.h |  4 ++
>  arch/arm64/include/asm/pgtable.h       |  2 +
>  virt/kvm/arm/mmu.c                     | 54 ++++++++++++++++++++------
>  5 files changed, 83 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 224c22c0a69c..155916dbdd7e 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -77,8 +77,11 @@ 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_pfn_pud(pfn, prot)	(__pud(0))
>  
>  #define kvm_pmd_mkhuge(pmd)	pmd_mkhuge(pmd)
> +/* No support for pud hugepages */
> +#define kvm_pud_mkhuge(pud)	(pud)
>  
>  /*
>   * The following kvm_*pud*() functionas are provided strictly to allow
> @@ -95,6 +98,22 @@ static inline bool kvm_s2pud_readonly(pud_t *pud)
>  	return false;
>  }
>  
> +static inline void kvm_set_pud(pud_t *pud, pud_t new_pud)
> +{
> +	BUG();
> +}
> +
> +static inline pud_t kvm_s2pud_mkwrite(pud_t pud)
> +{
> +	BUG();
> +	return pud;
> +}
> +
> +static inline pud_t kvm_s2pud_mkexec(pud_t pud)
> +{
> +	BUG();
> +	return pud;
> +}
>  
>  static inline void kvm_set_pmd(pmd_t *pmd, pmd_t new_pmd)
>  {
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index f440cf216a23..f49a68fcbf26 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -172,11 +172,14 @@ 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)
>  
>  #define kvm_pfn_pte(pfn, prot)		pfn_pte(pfn, prot)
>  #define kvm_pfn_pmd(pfn, prot)		pfn_pmd(pfn, prot)
> +#define kvm_pfn_pud(pfn, prot)		pfn_pud(pfn, prot)
>  
>  #define kvm_pmd_mkhuge(pmd)		pmd_mkhuge(pmd)
> +#define kvm_pud_mkhuge(pud)		pud_mkhuge(pud)
>  
>  static inline pte_t kvm_s2pte_mkwrite(pte_t pte)
>  {
> @@ -190,6 +193,12 @@ 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 pte_t kvm_s2pte_mkexec(pte_t pte)
>  {
>  	pte_val(pte) &= ~PTE_S2_XN;
> @@ -202,6 +211,12 @@ static inline pmd_t kvm_s2pmd_mkexec(pmd_t pmd)
>  	return pmd;
>  }
>  
> +static inline pud_t kvm_s2pud_mkexec(pud_t pud)
> +{
> +	pud_val(pud) &= ~PUD_S2_XN;
> +	return pud;
> +}
> +
>  static inline void kvm_set_s2pte_readonly(pte_t *ptep)
>  {
>  	pteval_t old_pteval, pteval;
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index fd208eac9f2a..e327665e94d1 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -193,6 +193,10 @@
>  #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_RDONLY		(_AT(pudval_t, 1) << 6)   /* HAP[2:1] */
> +#define PUD_S2_RDWR		(_AT(pudval_t, 3) << 6)   /* HAP[2:1] */
> +#define PUD_S2_XN		(_AT(pudval_t, 2) << 53)  /* XN[1:0] */
> +
>  /*
>   * 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 7e2c27e63cd8..5efb4585c879 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -386,6 +386,8 @@ static inline int pmd_protnone(pmd_t pmd)
>  
>  #define pud_write(pud)		pte_write(pud_pte(pud))
>  
> +#define pud_mkhuge(pud)		(__pud(pud_val(pud) & ~PUD_TABLE_BIT))
> +
>  #define __pud_to_phys(pud)	__pte_to_phys(pud_pte(pud))
>  #define __phys_to_pud_val(phys)	__phys_to_pte_val(phys)
>  #define pud_pfn(pud)		((__pud_to_phys(pud) & PUD_MASK) >> PAGE_SHIFT)
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 5f53909da90e..7fb58dca0a83 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -1036,6 +1036,26 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
>  	return 0;
>  }
>  
> +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);
> +
> +	old_pud = *pud;
> +	if (pud_present(old_pud)) {
> +		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 bool stage2_is_exec(struct kvm *kvm, phys_addr_t addr)
>  {
>  	pmd_t *pmdp;
> @@ -1452,9 +1472,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	}
>  
>  	vma_pagesize = vma_kernel_pagesize(vma);
> -	if (vma_pagesize == PMD_SIZE && !logging_active) {
> +	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
> @@ -1521,15 +1544,8 @@ 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) {
> -		/*
> -		 * Only PMD_SIZE transparent hugepages(THP) are
> -		 * currently supported. This code will need to be
> -		 * updated if other THP sizes are supported.
> -		 */
> +	if (!hugetlb && !force_pte)
>  		hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
> -		vma_pagesize = PMD_SIZE;

Why this change?  Won't you end up trying to map THPs as individual
pages now?

> -	}
>  
>  	if (writable)
>  		kvm_set_pfn_dirty(pfn);
> @@ -1540,7 +1556,23 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	if (exec_fault)
>  		invalidate_icache_guest_page(pfn, vma_pagesize);
>  
> -	if (hugetlb) {
> +	if (vma_pagesize == PUD_SIZE) {
> +		pud_t new_pud = kvm_pfn_pud(pfn, mem_type);
> +
> +		new_pud = kvm_pud_mkhuge(new_pud);
> +		if (writable)
> +			new_pud = kvm_s2pud_mkwrite(new_pud);
> +
> +		if (exec_fault) {
> +			new_pud = kvm_s2pud_mkexec(new_pud);
> +		} else if (fault_status == FSC_PERM) {
> +			/* Preserve execute if XN was already cleared */
> +			if (stage2_is_exec(kvm, fault_ipa))
> +				new_pud = kvm_s2pud_mkexec(new_pud);
> +		}

aha, another reason for my suggestion in the other patch.

> +
> +		ret = stage2_set_pud_huge(kvm, memcache, fault_ipa, &new_pud);
> +	} else if (vma_pagesize == PMD_SIZE) {
>  		pmd_t new_pmd = kvm_pfn_pmd(pfn, mem_type);
>  
>  		new_pmd = kvm_pmd_mkhuge(new_pmd);
> -- 
> 2.17.0
> 

Otherwise, this patch looks fine.

Thanks,
-Christoffer