Subject: [PATCH v15 11/11] KVM: arm/arm64: Add support to dissolve huge PUD

From: [email-masked] (Christoffer Dall)
Date: Wed, 7 Jan 2015 14:05:14 +0100

On Sun, Dec 14, 2014 at 11:28:08PM -0800, Mario Smarduch wrote:
> This patch adds the same support for PUD huge page as for PMD. Huge PUD is 
> write protected for initial memory region write protection. Code to dissolve 
> huge PUD is supported in user_mem_abort(). At this time this code has not been 
> tested, but similar approach to current ARMv8 page logging test is in work,
> limiting kernel memory and mapping in 1 or 2GB into Guest address space on a 
> 4k page/48 bit host, some host kernel test code needs to be added to detect
> page fault to this region and side step general processing. Also similar to 
> PMD case all pages in range are marked dirty when PUD entry is cleared.

the note about this code being untested shouldn't be part of the commit
message but after the '---' separater or in the cover letter I think.

> 
> Signed-off-by: Mario Smarduch <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_mmu.h         |  8 +++++
>  arch/arm/kvm/mmu.c                     | 64 ++++++++++++++++++++++++++++++++--
>  arch/arm64/include/asm/kvm_mmu.h       |  9 +++++
>  arch/arm64/include/asm/pgtable-hwdef.h |  3 ++
>  4 files changed, 81 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index dda0046..703d04d 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -133,6 +133,14 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
>  	return (pmd_val(*pmd) & L_PMD_S2_RDWR) == L_PMD_S2_RDONLY;
>  }
>  
> +static inline void kvm_set_s2pud_readonly(pud_t *pud)
> +{
> +}
> +
> +static inline bool kvm_s2pud_readonly(pud_t *pud)
> +{
> +	return false;
> +}
>  
>  /* Open coded p*d_addr_end that can deal with 64bit addresses */
>  #define kvm_pgd_addr_end(addr, end)					\
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 59003df..35840fb 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -109,6 +109,55 @@ void stage2_dissolve_pmd(struct kvm *kvm, phys_addr_t addr, pmd_t *pmd)
>  	}
>  }
>  
> +/**
> +  * stage2_find_pud() - find a PUD entry
> +  * @kvm:	pointer to kvm structure.
> +  * @addr:	IPA address
> +  *
> +  * Return address of PUD entry or NULL if not allocated.
> +  */
> +static pud_t *stage2_find_pud(struct kvm *kvm, phys_addr_t addr)

why can't you reuse stage2_get_pud here?

> +{
> +	pgd_t *pgd;
> +
> +	pgd = kvm->arch.pgd + pgd_index(addr);
> +	if (pgd_none(*pgd))
> +		return NULL;
> +
> +	return pud_offset(pgd, addr);
> +}
> +
> +/**
> + * stage2_dissolve_pud() - clear and flush huge PUD entry
> + * @kvm:	pointer to kvm structure.
> + * @addr	IPA
> + *
> + * Function clears a PUD entry, flushes addr 1st and 2nd stage TLBs. Marks all
> + * pages in the range dirty.
> + */
> +void stage2_dissolve_pud(struct kvm *kvm, phys_addr_t addr)
> +{
> +	pud_t *pud;
> +	gfn_t gfn;
> +	long i;
> +
> +	pud = stage2_find_pud(kvm, addr);
> +	if (pud && !pud_none(*pud) && kvm_pud_huge(*pud)) {

I'm just thinking here, why do we need to check if we get a valid pud
back here, but we don't need the equivalent check in dissolve_pmd from
patch 7?

I think the rationale is that it should never happen because we never
call these functions with the logging and iomap flags at the same
time...

> +		pud_clear(pud);
> +		kvm_tlb_flush_vmid_ipa(kvm, addr);
> +		put_page(virt_to_page(pud));
> +#ifdef CONFIG_SMP
> +		gfn = (addr & PUD_MASK) >> PAGE_SHIFT;
> +		/*
> +		 * Mark all pages in PUD range dirty, in case other
> +		 * CPUs are  writing to it.
> +		 */
> +		for (i = 0; i < PTRS_PER_PUD * PTRS_PER_PMD; i++)
> +			mark_page_dirty(kvm, gfn + i);
> +#endif
> +	}
> +}
> +
>  static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
>  				  int min, int max)
>  {
> @@ -761,6 +810,13 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
>  	unsigned long iomap = flags & KVM_S2PTE_FLAG_IS_IOMAP;
>  	unsigned long logging_active = flags & KVM_S2PTE_FLAG_LOGGING_ACTIVE;
>  
> +	/*
> +	 * While dirty page logging - dissolve huge PUD, then continue on to
> +	 * allocate page.
> +	 */
> +	if (logging_active)
> +		stage2_dissolve_pud(kvm, addr);
> +

I know I asked for this, but what's the purpose really when we never set
a huge stage-2 pud, shouldn't we just WARN/BUG if we encounter one?

Marc, you may have some thoughts here...

>  	/* Create stage-2 page table mapping - Levels 0 and 1 */
>  	pmd = stage2_get_pmd(kvm, cache, addr);
>  	if (!pmd) {
> @@ -964,9 +1020,11 @@ static void  stage2_wp_puds(pgd_t *pgd, phys_addr_t addr, phys_addr_t end)
>  	do {
>  		next = kvm_pud_addr_end(addr, end);
>  		if (!pud_none(*pud)) {
> -			/* TODO:PUD not supported, revisit later if supported */
> -			BUG_ON(kvm_pud_huge(*pud));
> -			stage2_wp_pmds(pud, addr, next);
> +			if (kvm_pud_huge(*pud)) {
> +				if (!kvm_s2pud_readonly(pud))
> +					kvm_set_s2pud_readonly(pud);

I guess the same question that I had above applies here as well (sorry
for making you go rounds on this one).

> +			} else
> +				stage2_wp_pmds(pud, addr, next);
>  		}
>  	} while (pud++, addr = next, addr != end);
>  }
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index f925e40..3b692c5 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -137,6 +137,15 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
>  	return (pmd_val(*pmd) & PMD_S2_RDWR) == PMD_S2_RDONLY;
>  }
>  
> +static inline void kvm_set_s2pud_readonly(pud_t *pud)
> +{
> +	pud_val(*pud) = (pud_val(*pud) & ~PUD_S2_RDWR) | PUD_S2_RDONLY;
> +}
> +
> +static inline bool kvm_s2pud_readonly(pud_t *pud)
> +{
> +	return (pud_val(*pud) & PUD_S2_RDWR) == PUD_S2_RDONLY;
> +}
>  
>  #define kvm_pgd_addr_end(addr, end)	pgd_addr_end(addr, end)
>  #define kvm_pud_addr_end(addr, end)	pud_addr_end(addr, end)
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index 5f930cc..1714c84 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -122,6 +122,9 @@
>  #define PMD_S2_RDONLY		(_AT(pmdval_t, 1) << 6)   /* HAP[2:1] */
>  #define PMD_S2_RDWR		(_AT(pmdval_t, 3) << 6)   /* HAP[2:1] */
>  
> +#define PUD_S2_RDONLY		(_AT(pudval_t, 1) << 6)   /* HAP[2:1] */
> +#define PUD_S2_RDWR		(_AT(pudval_t, 3) << 6)   /* HAP[2:1] */
> +
>  /*
>   * Memory Attribute override for Stage-2 (MemAttr[3:0])
>   */
> -- 
> 1.9.1
>