Re: [PATCH v2 10/12] KVM: MMU: unify the code of walking pte list

[Gleb Natapov]

On Wed, Jan 23, 2013 at 06:09:34PM +0800, Xiao Guangrong wrote:
> Walking parent spte and walking ramp have same logic, this patch introduces
> for_each_spte_in_pte_list to integrate their code
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
>  arch/x86/kvm/mmu.c       |  199 ++++++++++++++++++++++------------------------
>  arch/x86/kvm/mmu_audit.c |    5 +-
>  2 files changed, 97 insertions(+), 107 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 55198a1..b7da3fb 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -968,26 +968,75 @@ static void pte_list_remove(u64 *spte, unsigned long *pte_list)
>  	}
>  }
> 
> -typedef void (*pte_list_walk_fn) (u64 *spte);
> -static void pte_list_walk(unsigned long *pte_list, pte_list_walk_fn fn)
> +/*
> + * Used by the following functions to iterate through the sptes linked by a
> + * pte_list.  All fields are private and not assumed to be used outside.
> + */
> +struct pte_list_iterator {
> +	/* private fields */
> +	struct pte_list_desc *desc;	/* holds the sptep if not NULL */
> +	int pos;			/* index of the sptep */
> +};
> +
> +/*
> + * Iteration must be started by this function.  This should also be used after
> + * removing/dropping sptes from the pte_list link because in such cases the
> + * information in the itererator may not be valid.
> + *
> + * Returns sptep if found, NULL otherwise.
> + */
> +static u64 *pte_list_get_first(unsigned long pte_list,
> +			       struct pte_list_iterator *iter)
>  {
> -	struct pte_list_desc *desc;
> -	int i;
> +	if (!pte_list)
> +		return NULL;
> 
> -	if (!*pte_list)
> -		return;
> +	if (!(pte_list & 1)) {
> +		iter->desc = NULL;
> +		return (u64 *)pte_list;
> +	}
> 
> -	if (!(*pte_list & 1))
> -		return fn((u64 *)*pte_list);
> +	iter->desc = (struct pte_list_desc *)(pte_list & ~1ul);
> +	iter->pos = 0;
> +	return iter->desc->sptes[iter->pos];
> +}
> 
> -	desc = (struct pte_list_desc *)(*pte_list & ~1ul);
> -	while (desc) {
> -		for (i = 0; i < PTE_LIST_EXT && desc->sptes[i]; ++i)
> -			fn(desc->sptes[i]);
> -		desc = desc->more;
> +/*
> + * Must be used with a valid iterator: e.g. after pte_list_get_next().
> + *
> + * Returns sptep if found, NULL otherwise.
> + */
> +static u64 *pte_list_get_next(struct pte_list_iterator *iter)
> +{
> +	if (iter->desc) {
> +		if (iter->pos < PTE_LIST_EXT - 1) {
> +			u64 *sptep;
> +
> +			++iter->pos;
> +			sptep = iter->desc->sptes[iter->pos];
> +			if (sptep)
> +				return sptep;
> +		}
> +
> +		iter->desc = iter->desc->more;
> +
> +		if (iter->desc) {
> +			iter->pos = 0;
> +			/* desc->sptes[0] cannot be NULL */
> +			return iter->desc->sptes[iter->pos];
> +		}
>  	}
> +
> +	return NULL;
>  }
> 
> +#define for_each_spte_in_pte_list(pte_list, iter, spte)		\
> +	   for (spte = pte_list_get_first(pte_list, &(iter));	\
> +	      spte != NULL; spte = pte_list_get_next(&(iter)))
> +
> +#define for_each_spte_in_rmap(rmap, iter, spte)			\
> +	   for_each_spte_in_pte_list(rmap, iter, spte)
> +
>  static unsigned long *__gfn_to_rmap(gfn_t gfn, int level,
>  				    struct kvm_memory_slot *slot)
>  {
> @@ -1039,67 +1088,6 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
>  	pte_list_remove(spte, rmapp);
>  }
> 
> -/*
> - * Used by the following functions to iterate through the sptes linked by a
> - * rmap.  All fields are private and not assumed to be used outside.
> - */
> -struct rmap_iterator {
> -	/* private fields */
> -	struct pte_list_desc *desc;	/* holds the sptep if not NULL */
> -	int pos;			/* index of the sptep */
> -};
> -
> -/*
> - * Iteration must be started by this function.  This should also be used after
> - * removing/dropping sptes from the rmap link because in such cases the
> - * information in the itererator may not be valid.
> - *
> - * Returns sptep if found, NULL otherwise.
> - */
> -static u64 *rmap_get_first(unsigned long rmap, struct rmap_iterator *iter)
> -{
> -	if (!rmap)
> -		return NULL;
> -
> -	if (!(rmap & 1)) {
> -		iter->desc = NULL;
> -		return (u64 *)rmap;
> -	}
> -
> -	iter->desc = (struct pte_list_desc *)(rmap & ~1ul);
> -	iter->pos = 0;
> -	return iter->desc->sptes[iter->pos];
> -}
> -
> -/*
> - * Must be used with a valid iterator: e.g. after rmap_get_first().
> - *
> - * Returns sptep if found, NULL otherwise.
> - */
> -static u64 *rmap_get_next(struct rmap_iterator *iter)
> -{
> -	if (iter->desc) {
> -		if (iter->pos < PTE_LIST_EXT - 1) {
> -			u64 *sptep;
> -
> -			++iter->pos;
> -			sptep = iter->desc->sptes[iter->pos];
> -			if (sptep)
> -				return sptep;
> -		}
> -
> -		iter->desc = iter->desc->more;
> -
> -		if (iter->desc) {
> -			iter->pos = 0;
> -			/* desc->sptes[0] cannot be NULL */
> -			return iter->desc->sptes[iter->pos];
> -		}
> -	}
> -
> -	return NULL;
> -}
> -
>  static void drop_spte(struct kvm *kvm, u64 *sptep)
>  {
>  	if (mmu_spte_clear_track_bits(sptep))
> @@ -1160,14 +1148,13 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
>  				 bool pt_protect)
>  {
>  	u64 *sptep;
> -	struct rmap_iterator iter;
> +	struct pte_list_iterator iter;
>  	bool flush = false;
> 
> -	for (sptep = rmap_get_first(*rmapp, &iter); sptep;) {
> +	for_each_spte_in_rmap(*rmapp, iter, sptep) {
>  		BUG_ON(!(*sptep & PT_PRESENT_MASK));
> 
>  		spte_write_protect(kvm, sptep, &flush, pt_protect);
> -		sptep = rmap_get_next(&iter);
>  	}
> 
>  	return flush;
> @@ -1221,15 +1208,14 @@ static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp,
>  			   struct kvm_memory_slot *slot, unsigned long data)
>  {
>  	u64 *sptep;
> -	struct rmap_iterator iter;
> +	struct pte_list_iterator iter;
>  	int need_tlb_flush = 0;
> 
> -	while ((sptep = rmap_get_first(*rmapp, &iter))) {
> -		BUG_ON(!(*sptep & PT_PRESENT_MASK));
> -		rmap_printk("kvm_rmap_unmap_hva: spte %p %llx\n", sptep, *sptep);
> -
> +restart:
> +	for_each_spte_in_rmap(*rmapp, iter, sptep) {
>  		drop_spte(kvm, sptep);
>  		need_tlb_flush = 1;
> +		goto restart;
>  	}
> 
>  	return need_tlb_flush;
> @@ -1239,7 +1225,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
>  			     struct kvm_memory_slot *slot, unsigned long data)
>  {
>  	u64 *sptep;
> -	struct rmap_iterator iter;
> +	struct pte_list_iterator iter;
>  	int need_flush = 0;
>  	u64 new_spte;
>  	pte_t *ptep = (pte_t *)data;
> @@ -1248,7 +1234,8 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
>  	WARN_ON(pte_huge(*ptep));
>  	new_pfn = pte_pfn(*ptep);
> 
> -	for (sptep = rmap_get_first(*rmapp, &iter); sptep;) {
> +restart:
> +	for_each_spte_in_rmap(*rmapp, iter, sptep) {
>  		BUG_ON(!is_shadow_present_pte(*sptep));
>  		rmap_printk("kvm_set_pte_rmapp: spte %p %llx\n", sptep, *sptep);
> 
> @@ -1256,19 +1243,18 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
> 
>  		if (pte_write(*ptep)) {
>  			drop_spte(kvm, sptep);
> -			sptep = rmap_get_first(*rmapp, &iter);
> -		} else {
> -			new_spte = *sptep & ~PT64_BASE_ADDR_MASK;
> -			new_spte |= (u64)new_pfn << PAGE_SHIFT;
> +			goto restart;
I do not like this "goto restart" pattern throughout this patch. Follow up
patch gets rid of most of them, so they are tolerable as a temporary solution
here, but this one stays. What about moving pte_write(*ptep) outside
for_each_spte_in_rmap() loop like that:

if (pte_write(*ptep))
	need_flush = kvm_unmap_rmapp();
else
	for_each_spte_in_rmap() {
	}

> +		}
> 
> -			new_spte &= ~PT_WRITABLE_MASK;
> -			new_spte &= ~SPTE_HOST_WRITEABLE;
> -			new_spte &= ~shadow_accessed_mask;
> +		new_spte = *sptep & ~PT64_BASE_ADDR_MASK;
> +		new_spte |= (u64)new_pfn << PAGE_SHIFT;
> 
> -			mmu_spte_clear_track_bits(sptep);
> -			mmu_spte_set(sptep, new_spte);
> -			sptep = rmap_get_next(&iter);
> -		}
> +		new_spte &= ~PT_WRITABLE_MASK;
> +		new_spte &= ~SPTE_HOST_WRITEABLE;
> +		new_spte &= ~shadow_accessed_mask;
> +
> +		mmu_spte_clear_track_bits(sptep);
> +		mmu_spte_set(sptep, new_spte);
>  	}
> 
>  	if (need_flush)
> @@ -1359,7 +1345,7 @@ static int kvm_age_rmapp(struct kvm *kvm, unsigned long *rmapp,
>  			 struct kvm_memory_slot *slot, unsigned long data)
>  {
>  	u64 *sptep;
> -	struct rmap_iterator uninitialized_var(iter);
> +	struct pte_list_iterator uninitialized_var(iter);
>  	int young = 0;
> 
>  	/*
> @@ -1375,8 +1361,7 @@ static int kvm_age_rmapp(struct kvm *kvm, unsigned long *rmapp,
>  		goto out;
>  	}
> 
> -	for (sptep = rmap_get_first(*rmapp, &iter); sptep;
> -	     sptep = rmap_get_next(&iter)) {
> +	for_each_spte_in_rmap(*rmapp, iter, sptep) {
>  		BUG_ON(!is_shadow_present_pte(*sptep));
> 
>  		if (*sptep & shadow_accessed_mask) {
> @@ -1395,7 +1380,7 @@ static int kvm_test_age_rmapp(struct kvm *kvm, unsigned long *rmapp,
>  			      struct kvm_memory_slot *slot, unsigned long data)
>  {
>  	u64 *sptep;
> -	struct rmap_iterator iter;
> +	struct pte_list_iterator iter;
>  	int young = 0;
> 
>  	/*
> @@ -1406,8 +1391,7 @@ static int kvm_test_age_rmapp(struct kvm *kvm, unsigned long *rmapp,
>  	if (!shadow_accessed_mask)
>  		goto out;
> 
> -	for (sptep = rmap_get_first(*rmapp, &iter); sptep;
> -	     sptep = rmap_get_next(&iter)) {
> +	for_each_spte_in_rmap(*rmapp, iter, sptep) {
>  		BUG_ON(!is_shadow_present_pte(*sptep));
> 
>  		if (*sptep & shadow_accessed_mask) {
> @@ -1539,7 +1523,11 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
>  static void mark_unsync(u64 *spte);
>  static void kvm_mmu_mark_parents_unsync(struct kvm_mmu_page *sp)
>  {
> -	pte_list_walk(&sp->parent_ptes, mark_unsync);
> +	struct pte_list_iterator iter;
> +	u64 *spte;
> +
> +	for_each_spte_in_pte_list(sp->parent_ptes, iter, spte)
> +		mark_unsync(spte);
>  }
> 
>  static void mark_unsync(u64 *spte)
> @@ -2059,10 +2047,13 @@ static void kvm_mmu_page_unlink_children(struct kvm *kvm,
>  static void kvm_mmu_unlink_parents(struct kvm *kvm, struct kvm_mmu_page *sp)
>  {
>  	u64 *sptep;
> -	struct rmap_iterator iter;
> +	struct pte_list_iterator iter;
> 
> -	while ((sptep = rmap_get_first(sp->parent_ptes, &iter)))
> +restart:
> +	for_each_spte_in_rmap(sp->parent_ptes, iter, sptep) {
>  		drop_parent_pte(sp, sptep);
> +		goto restart;
> +	}
>  }
> 
>  static int mmu_zap_unsync_children(struct kvm *kvm,
> diff --git a/arch/x86/kvm/mmu_audit.c b/arch/x86/kvm/mmu_audit.c
> index daff69e..a08d384 100644
> --- a/arch/x86/kvm/mmu_audit.c
> +++ b/arch/x86/kvm/mmu_audit.c
> @@ -190,15 +190,14 @@ static void audit_write_protection(struct kvm *kvm, struct kvm_mmu_page *sp)
>  {
>  	unsigned long *rmapp;
>  	u64 *sptep;
> -	struct rmap_iterator iter;
> +	struct pte_list_iterator iter;
> 
>  	if (sp->role.direct || sp->unsync || sp->role.invalid)
>  		return;
> 
>  	rmapp = gfn_to_rmap(kvm, sp->gfn, PT_PAGE_TABLE_LEVEL);
> 
> -	for (sptep = rmap_get_first(*rmapp, &iter); sptep;
> -	     sptep = rmap_get_next(&iter)) {
> +	for_each_spte_in_rmap(*rmapp, iter, sptep) {
>  		if (is_writable_pte(*sptep))
>  			audit_printk(kvm, "shadow page has writable "
>  				     "mappings: gfn %llx role %x\n",
> -- 
> 1.7.7.6

--
			Gleb.
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