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KVM: MMU: do not need atomicly to set/clear spte

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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>
This commit is contained in:
Xiao Guangrong 2011-07-12 03:31:28 +08:00 committed by Avi Kivity
parent 1df9f2dc39
commit 603e0651cf
1 changed files with 74 additions and 18 deletions
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92
arch/x86/kvm/mmu.c
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@ -259,26 +259,82 @@ static gfn_t pse36_gfn_delta(u32 gpte)
return (gpte & PT32_DIR_PSE36_MASK) << shift;
}
#ifdef CONFIG_X86_64
static void __set_spte(u64 *sptep, u64 spte)
{
set_64bit(sptep, spte);
*sptep = spte;
}
static u64 __xchg_spte(u64 *sptep, u64 new_spte)
static void __update_clear_spte_fast(u64 *sptep, u64 spte)
{
#ifdef CONFIG_X86_64
return xchg(sptep, new_spte);
#else
u64 old_spte;
do {
old_spte = *sptep;
} while (cmpxchg64(sptep, old_spte, new_spte) != old_spte);
return old_spte;
#endif
*sptep = spte;
}
static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)
{
return xchg(sptep, spte);
}
#else
union split_spte {
struct {
u32 spte_low;
u32 spte_high;
};
u64 spte;
};
static void __set_spte(u64 *sptep, u64 spte)
{
union split_spte *ssptep, sspte;
ssptep = (union split_spte *)sptep;
sspte = (union split_spte)spte;
ssptep->spte_high = sspte.spte_high;
/*
* If we map the spte from nonpresent to present, We should store
* the high bits firstly, then set present bit, so cpu can not
* fetch this spte while we are setting the spte.
*/
smp_wmb();
ssptep->spte_low = sspte.spte_low;
}
static void __update_clear_spte_fast(u64 *sptep, u64 spte)
{
union split_spte *ssptep, sspte;
ssptep = (union split_spte *)sptep;
sspte = (union split_spte)spte;
ssptep->spte_low = sspte.spte_low;
/*
* If we map the spte from present to nonpresent, we should clear
* present bit firstly to avoid vcpu fetch the old high bits.
*/
smp_wmb();
ssptep->spte_high = sspte.spte_high;
}
static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)
{
union split_spte *ssptep, sspte, orig;
ssptep = (union split_spte *)sptep;
sspte = (union split_spte)spte;
/* xchg acts as a barrier before the setting of the high bits */
orig.spte_low = xchg(&ssptep->spte_low, sspte.spte_low);
orig.spte_high = ssptep->spte_high = sspte.spte_high;
return orig.spte;
}
#endif
static bool spte_has_volatile_bits(u64 spte)
{
if (!shadow_accessed_mask)
@ -330,9 +386,9 @@ static void mmu_spte_update(u64 *sptep, u64 new_spte)
mask |= shadow_dirty_mask;
if (!spte_has_volatile_bits(old_spte) || (new_spte & mask) == mask)
__set_spte(sptep, new_spte);
__update_clear_spte_fast(sptep, new_spte);
else
old_spte = __xchg_spte(sptep, new_spte);
old_spte = __update_clear_spte_slow(sptep, new_spte);
if (!shadow_accessed_mask)
return;
@ -354,9 +410,9 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
u64 old_spte = *sptep;
if (!spte_has_volatile_bits(old_spte))
__set_spte(sptep, 0ull);
__update_clear_spte_fast(sptep, 0ull);
else
old_spte = __xchg_spte(sptep, 0ull);
old_spte = __update_clear_spte_slow(sptep, 0ull);
if (!is_rmap_spte(old_spte))
return 0;
@ -376,7 +432,7 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
*/
static void mmu_spte_clear_no_track(u64 *sptep)
{
__set_spte(sptep, 0ull);
__update_clear_spte_fast(sptep, 0ull);
}
static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,