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Commit 603e0651 authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Avi Kivity
Browse files

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: default avatarXiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 1df9f2dc

arch/x86/kvm/mmu.c

+71 −15
Original line number Diff line number Diff line
@@ -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);

	*sptep = spte;

}



static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)

{

	return xchg(sptep, spte);

}

#else

	u64 old_spte;

union split_spte {

	struct {

		u32 spte_low;

		u32 spte_high;

	};

	u64 spte;

};



	do {

		old_spte = *sptep;

	} while (cmpxchg64(sptep, old_spte, new_spte) != old_spte);

static void __set_spte(u64 *sptep, u64 spte)

{

	union split_spte *ssptep, sspte;



	return old_spte;

#endif

	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,