On 04/16/2012 06:25 AM, Xiao Guangrong wrote: > 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
It's overloading me :( > 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. The fast page fault path is supposed to be fast, so it's okay if we take a bit of extra overhead before a COW (which is going to be slow anyway). Let's get the simplest possible version in, and then discuss if/how we need to optimize it further. -- error compiling committee.c: too many arguments to function -- 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
