On 04/15/2012 11:16 PM, Avi Kivity wrote: > On 04/13/2012 01:14 PM, Xiao Guangrong wrote: >> Using bit 1 (PTE_LIST_WP_BIT) in rmap store the write-protect status >> to avoid unnecessary shadow page walking >> >> Signed-off-by: Xiao Guangrong <[email protected]> >> --- >> arch/x86/kvm/mmu.c | 40 ++++++++++++++++++++++++++++++++++------ >> 1 files changed, 34 insertions(+), 6 deletions(-) >> >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index 0c6e92d..8b71908 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -796,7 +796,9 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t >> large_gfn) >> return level - 1; >> } >> >> -#define PTE_LIST_DESC (0x1ull) >> +#define PTE_LIST_DESC_BIT 0 >> +#define PTE_LIST_WP_BIT 1 >> +#define PTE_LIST_DESC (1 << PTE_LIST_DESC_BIT) >> #define PTE_LIST_FLAG_MASK (0x3ull) >> >> static void >> @@ -1067,6 +1069,12 @@ static bool rmap_can_add(struct kvm_vcpu *vcpu) >> return mmu_memory_cache_free_objects(cache); >> } >> >> +static void host_page_write_protect(u64 *spte, unsigned long *rmapp) >> +{ >> + if (!(*spte & SPTE_HOST_WRITEABLE)) >> + __test_and_set_bit(PTE_LIST_WP_BIT, rmapp); >> +} >> > > Why is this needed, in addition to spte.SPTE_WRITE_PROTECT? >
It is used to avoid the unnecessary overload for fast page fault if KSM is enabled. On the fast check path, it can see the gfn is write-protected by host, then the fast page fault path is not called. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
