On 04/16/2012 06:02 PM, Avi Kivity wrote: > 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 :( >
Sorry. >> 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. > Okay, i will drop setting PTE_LIST_WP_BIT for this case in the next version.:) -- 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
