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KVM: MMU: do not need atomicly to set/clear spte
Now, the spte is just from nonprsent to present or present to nonprsent, so we can use some trick to set/clear spte non-atomicly as linux kernel does Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> Signed-off-by: Avi Kivity <avi@redhat.com>
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@ -259,26 +259,82 @@ static gfn_t pse36_gfn_delta(u32 gpte)
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return (gpte & PT32_DIR_PSE36_MASK) << shift;
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}
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#ifdef CONFIG_X86_64
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static void __set_spte(u64 *sptep, u64 spte)
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{
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set_64bit(sptep, spte);
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*sptep = spte;
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}
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static u64 __xchg_spte(u64 *sptep, u64 new_spte)
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static void __update_clear_spte_fast(u64 *sptep, u64 spte)
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{
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#ifdef CONFIG_X86_64
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return xchg(sptep, new_spte);
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#else
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u64 old_spte;
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do {
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old_spte = *sptep;
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} while (cmpxchg64(sptep, old_spte, new_spte) != old_spte);
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return old_spte;
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#endif
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*sptep = spte;
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}
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static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)
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{
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return xchg(sptep, spte);
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}
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#else
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union split_spte {
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struct {
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u32 spte_low;
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u32 spte_high;
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};
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u64 spte;
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};
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static void __set_spte(u64 *sptep, u64 spte)
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{
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union split_spte *ssptep, sspte;
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ssptep = (union split_spte *)sptep;
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sspte = (union split_spte)spte;
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ssptep->spte_high = sspte.spte_high;
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/*
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* If we map the spte from nonpresent to present, We should store
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* the high bits firstly, then set present bit, so cpu can not
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* fetch this spte while we are setting the spte.
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*/
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smp_wmb();
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ssptep->spte_low = sspte.spte_low;
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}
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static void __update_clear_spte_fast(u64 *sptep, u64 spte)
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{
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union split_spte *ssptep, sspte;
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ssptep = (union split_spte *)sptep;
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sspte = (union split_spte)spte;
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ssptep->spte_low = sspte.spte_low;
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/*
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* If we map the spte from present to nonpresent, we should clear
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* present bit firstly to avoid vcpu fetch the old high bits.
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*/
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smp_wmb();
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ssptep->spte_high = sspte.spte_high;
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}
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static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)
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{
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union split_spte *ssptep, sspte, orig;
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ssptep = (union split_spte *)sptep;
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sspte = (union split_spte)spte;
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/* xchg acts as a barrier before the setting of the high bits */
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orig.spte_low = xchg(&ssptep->spte_low, sspte.spte_low);
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orig.spte_high = ssptep->spte_high = sspte.spte_high;
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return orig.spte;
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}
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#endif
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static bool spte_has_volatile_bits(u64 spte)
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{
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if (!shadow_accessed_mask)
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@ -330,9 +386,9 @@ static void mmu_spte_update(u64 *sptep, u64 new_spte)
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mask |= shadow_dirty_mask;
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if (!spte_has_volatile_bits(old_spte) || (new_spte & mask) == mask)
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__set_spte(sptep, new_spte);
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__update_clear_spte_fast(sptep, new_spte);
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else
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old_spte = __xchg_spte(sptep, new_spte);
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old_spte = __update_clear_spte_slow(sptep, new_spte);
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if (!shadow_accessed_mask)
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return;
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@ -354,9 +410,9 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
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u64 old_spte = *sptep;
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if (!spte_has_volatile_bits(old_spte))
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__set_spte(sptep, 0ull);
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__update_clear_spte_fast(sptep, 0ull);
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else
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old_spte = __xchg_spte(sptep, 0ull);
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old_spte = __update_clear_spte_slow(sptep, 0ull);
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if (!is_rmap_spte(old_spte))
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return 0;
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@ -376,7 +432,7 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
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*/
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static void mmu_spte_clear_no_track(u64 *sptep)
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{
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__set_spte(sptep, 0ull);
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__update_clear_spte_fast(sptep, 0ull);
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}
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static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
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