From 83ef6c8155c0ecb4c1a7e6bfbe425c85f7cb676d Mon Sep 17 00:00:00 2001 From: Junaid Shahid Date: Tue, 6 Dec 2016 16:46:13 -0800 Subject: [PATCH] kvm: x86: mmu: Refactor accessed/dirty checks in mmu_spte_update/clear This simplifies mmu_spte_update() a little bit. The checks for clearing of accessed and dirty bits are refactored into separate functions, which are used inside both mmu_spte_update() and mmu_spte_clear_track_bits(), as well as kvm_test_age_rmapp(). The new helper functions handle both the case when A/D bits are supported in hardware and the case when they are not. Signed-off-by: Junaid Shahid Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu.c | 66 ++++++++++++++++++++++------------------------ 1 file changed, 31 insertions(+), 35 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index f6d3505c8d18..cfef95969335 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -504,14 +504,16 @@ static bool spte_has_volatile_bits(u64 spte) return true; } -static bool spte_is_bit_cleared(u64 old_spte, u64 new_spte, u64 bit_mask) +static bool is_accessed_spte(u64 spte) { - return (old_spte & bit_mask) && !(new_spte & bit_mask); + return shadow_accessed_mask ? spte & shadow_accessed_mask + : true; } -static bool spte_is_bit_changed(u64 old_spte, u64 new_spte, u64 bit_mask) +static bool is_dirty_spte(u64 spte) { - return (old_spte & bit_mask) != (new_spte & bit_mask); + return shadow_dirty_mask ? spte & shadow_dirty_mask + : spte & PT_WRITABLE_MASK; } /* Rules for using mmu_spte_set: @@ -534,17 +536,19 @@ static void mmu_spte_set(u64 *sptep, u64 new_spte) * will find a read-only spte, even though the writable spte * might be cached on a CPU's TLB, the return value indicates this * case. + * + * Returns true if the TLB needs to be flushed */ static bool mmu_spte_update(u64 *sptep, u64 new_spte) { u64 old_spte = *sptep; - bool ret = false; + bool flush = false; WARN_ON(!is_shadow_present_pte(new_spte)); if (!is_shadow_present_pte(old_spte)) { mmu_spte_set(sptep, new_spte); - return ret; + return flush; } if (!spte_has_volatile_bits(old_spte)) @@ -552,6 +556,8 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte) else old_spte = __update_clear_spte_slow(sptep, new_spte); + WARN_ON(spte_to_pfn(old_spte) != spte_to_pfn(new_spte)); + /* * For the spte updated out of mmu-lock is safe, since * we always atomically update it, see the comments in @@ -559,38 +565,31 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte) */ if (spte_can_locklessly_be_made_writable(old_spte) && !is_writable_pte(new_spte)) - ret = true; - - if (!shadow_accessed_mask) { - /* - * We don't set page dirty when dropping non-writable spte. - * So do it now if the new spte is becoming non-writable. - */ - if (ret) - kvm_set_pfn_dirty(spte_to_pfn(old_spte)); - return ret; - } + flush = true; /* - * Flush TLB when accessed/dirty bits are changed in the page tables, + * Flush TLB when accessed/dirty states are changed in the page tables, * to guarantee consistency between TLB and page tables. */ - if (spte_is_bit_changed(old_spte, new_spte, - shadow_accessed_mask | shadow_dirty_mask)) - ret = true; - if (spte_is_bit_cleared(old_spte, new_spte, shadow_accessed_mask)) + if (is_accessed_spte(old_spte) && !is_accessed_spte(new_spte)) { + flush = true; kvm_set_pfn_accessed(spte_to_pfn(old_spte)); - if (spte_is_bit_cleared(old_spte, new_spte, shadow_dirty_mask)) + } + + if (is_dirty_spte(old_spte) && !is_dirty_spte(new_spte)) { + flush = true; kvm_set_pfn_dirty(spte_to_pfn(old_spte)); + } - return ret; + return flush; } /* * Rules for using mmu_spte_clear_track_bits: * It sets the sptep from present to nonpresent, and track the * state bits, it is used to clear the last level sptep. + * Returns non-zero if the PTE was previously valid. */ static int mmu_spte_clear_track_bits(u64 *sptep) { @@ -614,11 +613,12 @@ static int mmu_spte_clear_track_bits(u64 *sptep) */ WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn))); - if (!shadow_accessed_mask || old_spte & shadow_accessed_mask) + if (is_accessed_spte(old_spte)) kvm_set_pfn_accessed(pfn); - if (old_spte & (shadow_dirty_mask ? shadow_dirty_mask : - PT_WRITABLE_MASK)) + + if (is_dirty_spte(old_spte)) kvm_set_pfn_dirty(pfn); + return 1; } @@ -1616,7 +1616,6 @@ static int kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head, { u64 *sptep; struct rmap_iterator iter; - int young = 0; /* * If there's no access bit in the secondary pte set by the @@ -1626,14 +1625,11 @@ static int kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head, if (!shadow_accessed_mask) goto out; - for_each_rmap_spte(rmap_head, &iter, sptep) { - if (*sptep & shadow_accessed_mask) { - young = 1; - break; - } - } + for_each_rmap_spte(rmap_head, &iter, sptep) + if (is_accessed_spte(*sptep)) + return 1; out: - return young; + return 0; } #define RMAP_RECYCLE_THRESHOLD 1000 -- 2.30.2