Subject: [PATCH v2] arm/arm64: KVM: Fix and refactor unmap_range

From: [email-masked] (Christoffer Dall)
Date: Wed, 4 Jun 2014 15:22:51 +0200

On Mon, Jun 02, 2014 at 10:29:51AM -0700, Mario Smarduch wrote:
> On 05/28/2014 07:22 AM, Christoffer Dall wrote:
> > unmap_range() was utterly broken, to quote Marc, and broke in all sorts
> > of situations.  It was also quite complicated to follow and didn't
> > follow the usual scheme of having a separate iterating function for each
> > level of page tables.
> > 
> > Address this by refactoring the code and introduce a pgd_clear()
> > function.
> > 
> > Acked-by: Marc Zyngier <[email-masked]>
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > ---
> > Changes since v2:
> >  - Don't define custom __unused but reuse __maybe_unused
> > 
> >  arch/arm/include/asm/kvm_mmu.h   |  12 ++++
> >  arch/arm/kvm/mmu.c               | 122 ++++++++++++++++++++++-----------------
> >  arch/arm64/include/asm/kvm_mmu.h |  15 +++++
> >  3 files changed, 95 insertions(+), 54 deletions(-)
> > 
> > diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> > index 5c7aa3c..5cc0b0f 100644
> > --- a/arch/arm/include/asm/kvm_mmu.h
> > +++ b/arch/arm/include/asm/kvm_mmu.h
> > @@ -127,6 +127,18 @@ static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
> >  	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
> >  })
> >  
> > +static inline bool kvm_page_empty(void *ptr)
> > +{
> > +	struct page *ptr_page = virt_to_page(ptr);
> > +	return page_count(ptr_page) == 1;
> > +}
> > +
> > +
> > +#define kvm_pte_table_empty(ptep) kvm_page_empty(ptep)
> > +#define kvm_pmd_table_empty(pmdp) kvm_page_empty(pmdp)
> > +#define kvm_pud_table_empty(pudp) (0)
> > +
> > +
> >  struct kvm;
> >  
> >  #define kvm_flush_dcache_to_poc(a,l)	__cpuc_flush_dcache_area((a), (l))
> > diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> > index 16f8049..6ee6e06 100644
> > --- a/arch/arm/kvm/mmu.c
> > +++ b/arch/arm/kvm/mmu.c
> > @@ -90,10 +90,13 @@ static void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc)
> >  	return p;
> >  }
> >  
> > -static bool page_empty(void *ptr)
> > +static void clear_pgd_entry(struct kvm *kvm, pgd_t *pgd, phys_addr_t addr)
> >  {
> > -	struct page *ptr_page = virt_to_page(ptr);
> > -	return page_count(ptr_page) == 1;
> > +	pud_t *pud_table __maybe_unused = pud_offset(pgd, 0);
> > +	pgd_clear(pgd);
> > +	kvm_tlb_flush_vmid_ipa(kvm, addr);
> > +	pud_free(NULL, pud_table);
> > +	put_page(virt_to_page(pgd));
> >  }
> >  
> >  static void clear_pud_entry(struct kvm *kvm, pud_t *pud, phys_addr_t addr)
> > @@ -124,70 +127,81 @@ static void clear_pmd_entry(struct kvm *kvm, pmd_t *pmd, phys_addr_t addr)
> >  	put_page(virt_to_page(pmd));
> >  }
> >  
> > -static void clear_pte_entry(struct kvm *kvm, pte_t *pte, phys_addr_t addr)
> > +static void unmap_ptes(struct kvm *kvm, pmd_t *pmd,
> > +		       unsigned long long addr, unsigned long long end)
> >  {
> > -	if (pte_present(*pte)) {
> > -		kvm_set_pte(pte, __pte(0));
> > -		put_page(virt_to_page(pte));
> > -		kvm_tlb_flush_vmid_ipa(kvm, addr);
> > -	}
> > +	pte_t *pte, *start_pte;
> > +	unsigned long long start_addr = addr;
> > +
> > +	start_pte = pte = pte_offset_kernel(pmd, addr);
> > +	do {
> > +		if (!pte_none(*pte)) {
> > +			kvm_set_pte(pte, __pte(0));
> > +			put_page(virt_to_page(pte));
> > +			kvm_tlb_flush_vmid_ipa(kvm, addr);
> > +		}
> > +	} while (pte++, addr += PAGE_SIZE, addr != end);
> > +
> > +	if (kvm_pte_table_empty(start_pte))
> > +		clear_pmd_entry(kvm, pmd, start_addr);
> >  }
> >  
> > -static void unmap_range(struct kvm *kvm, pgd_t *pgdp,
> > -			unsigned long long start, u64 size)
> > +static void unmap_pmds(struct kvm *kvm, pud_t *pud,
> > +		       unsigned long long addr, unsigned long long end)
> >  {
> > -	pgd_t *pgd;
> > -	pud_t *pud;
> > -	pmd_t *pmd;
> > -	pte_t *pte;
> > -	unsigned long long addr = start, end = start + size;
> > -	u64 next;
> > -
> > -	while (addr < end) {
> > -		pgd = pgdp + pgd_index(addr);
> > -		pud = pud_offset(pgd, addr);
> > -		pte = NULL;
> > -		if (pud_none(*pud)) {
> > -			addr = kvm_pud_addr_end(addr, end);
> > -			continue;
> > -		}
> > +	unsigned long long next, start_addr = addr;
> > +	pmd_t *pmd, *start_pmd;
> >  
> > -		if (pud_huge(*pud)) {
> > -			/*
> > -			 * If we are dealing with a huge pud, just clear it and
> > -			 * move on.
> > -			 */
> > -			clear_pud_entry(kvm, pud, addr);
> > -			addr = kvm_pud_addr_end(addr, end);
> > -			continue;
> > +	start_pmd = pmd = pmd_offset(pud, addr);
> > +	do {
> > +		next = kvm_pmd_addr_end(addr, end);
> > +		if (!pmd_none(*pmd)) {
> > +			if (kvm_pmd_huge(*pmd))
> > +				clear_pmd_entry(kvm, pmd, addr);
> > +			else
> > +				unmap_ptes(kvm, pmd, addr, next);
> >  		}
> > +	} while (pmd++, addr = next, addr != end);
> >  
> > -		pmd = pmd_offset(pud, addr);
> > -		if (pmd_none(*pmd)) {
> > -			addr = kvm_pmd_addr_end(addr, end);
> > -			continue;
> > -		}
> > +	if (kvm_pmd_table_empty(start_pmd))
> > +		clear_pud_entry(kvm, pud, start_addr);
> > +}
> >  
> > -		if (!kvm_pmd_huge(*pmd)) {
> > -			pte = pte_offset_kernel(pmd, addr);
> > -			clear_pte_entry(kvm, pte, addr);
> > -			next = addr + PAGE_SIZE;
> > -		}
> > +static void unmap_puds(struct kvm *kvm, pgd_t *pgd,
> > +		       unsigned long long addr, unsigned long long end)
> > +{
> > +	unsigned long long next, start_addr = addr;
> > +	pud_t *pud, *start_pud;
> >  
> > -		/*
> > -		 * If the pmd entry is to be cleared, walk back up the ladder
> > -		 */
> > -		if (kvm_pmd_huge(*pmd) || (pte && page_empty(pte))) {
> > -			clear_pmd_entry(kvm, pmd, addr);
> > -			next = kvm_pmd_addr_end(addr, end);
> > -			if (page_empty(pmd) && !page_empty(pud)) {
> > +	start_pud = pud = pud_offset(pgd, addr);
> > +	do {
> > +		next = kvm_pud_addr_end(addr, end);
> > +		if (!pud_none(*pud)) {
> > +			if (pud_huge(*pid)) {
> 
> The *pid breaks build, assuming *pud here.
> 

ah, right, thanks for spotting it.

> >  				clear_pud_entry(kvm, pud, addr);
> > -				next = kvm_pud_addr_end(addr, end);
> > +			} else {
> > +				unmap_pmds(kvm, pud, addr, next);
> >  			}
> I minor one but I figure I mention it, checkpatch.pl complains 
> about the unnecessary braces

and it's right, I've corrected it.

> >  		}
> > +	} while (pud++, addr = next, addr != end);
> >  
> > -		addr = next;
> > -	}
> > +	if (kvm_pud_table_empty(start_pud))
> > +		clear_pgd_entry(kvm, pgd, start_addr);
> > +}
> > +
> > +
> > +static void unmap_range(struct kvm *kvm, pgd_t *pgdp,
> > +			unsigned long long start, u64 size)
> > +{
> > +	pgd_t *pgd;
> > +	unsigned long long addr = start, end = start + size;
> > +	unsigned long long next;
> > +
> > +	pgd = pgdp + pgd_index(addr);
> > +	do {
> > +		next = kvm_pgd_addr_end(addr, end);
> > +		unmap_puds(kvm, pgd, addr, next);
> > +	} while (pgd++, addr = next, addr != end);
> >  }
> >  
> >  static void stage2_flush_ptes(struct kvm *kvm, pmd_t *pmd,
> > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> > index 7d29847..8e138c7 100644
> > --- a/arch/arm64/include/asm/kvm_mmu.h
> > +++ b/arch/arm64/include/asm/kvm_mmu.h
> > @@ -125,6 +125,21 @@ static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
> >  #define kvm_pud_addr_end(addr, end)	pud_addr_end(addr, end)
> >  #define kvm_pmd_addr_end(addr, end)	pmd_addr_end(addr, end)
> >  
> > +static inline bool kvm_page_empty(void *ptr)
> > +{
> > +	struct page *ptr_page = virt_to_page(ptr);
> > +	return page_count(ptr_page) == 1;
> > +}
> > +
> > +#define kvm_pte_table_empty(ptep) kvm_page_empty(ptep)
> > +#ifndef CONFIG_ARM64_64K_PAGES
> > +#define kvm_pmd_table_empty(pmdp) kvm_page_empty(pmdp)
> > +#else
> > +#define kvm_pmd_table_empty(pmdp) (0)
> > +#endif
> > +#define kvm_pud_table_empty(pudp) (0)
> > +
> > +
> >  struct kvm;
> >  
> >  #define kvm_flush_dcache_to_poc(a,l)	__flush_dcache_area((a), (l))
> > 
> 
> Tested on 4-way SMP with  page reclaim no problem seen.
> 
> Reviewed-by: Mario Smarduch <[email-masked]>
> 

Thanks,
-Christoffer