Re: [PATCH] KVM: MMU: Don't flush shadow when enabling dirty tracking

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On 12/27/2010 11:16 AM, Avi Kivity wrote:
On 12/27/2010 06:06 AM, Takuya Yoshikawa wrote:
Avi Kivity<avi@xxxxxxxxxx>  wrote:

> Instead, drop large mappings, which were the reason we dropped shadow.
>
>  Signed-off-by: Avi Kivity<avi@xxxxxxxxxx>
>  ---
>   arch/x86/kvm/mmu.c  |   10 ++++++----
>   virt/kvm/kvm_main.c |    7 +------
>   2 files changed, 7 insertions(+), 10 deletions(-)
>
>  diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>  index 43bd5e3..1bbe2c0 100644
>  --- a/arch/x86/kvm/mmu.c
>  +++ b/arch/x86/kvm/mmu.c
> @@ -3444,14 +3444,16 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
>           if (!test_bit(slot, sp->slot_bitmap))
>               continue;
>
>  -        if (sp->role.level != PT_PAGE_TABLE_LEVEL)
>  -            continue;
>  -
>           pt = sp->spt;
>  -        for (i = 0; i<  PT64_ENT_PER_PAGE; ++i)
>  +        for (i = 0; i<  PT64_ENT_PER_PAGE; ++i) {
>  +            if (sp->role.level != PT_PAGE_TABLE_LEVEL
>  + &&  is_large_pte(pt[i]))
>  +                drop_spte(kvm,&pt[i],
>  +                      shadow_trap_nonpresent_pte);
>               /* avoid RMW */
>               if (is_writable_pte(pt[i]))
>                   update_spte(&pt[i], pt[i]&  ~PT_WRITABLE_MASK);
>  +        }
>       }
>       kvm_flush_remote_tlbs(kvm);
>   }

What is the difference from the similar part in rmap_write_protect()?

=== from rmap_write_protect() ===

    /* check for huge page mappings */
    for (i = PT_DIRECTORY_LEVEL;
         i<  PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) {
        rmapp = gfn_to_rmap(kvm, gfn, i);
        spte = rmap_next(kvm, rmapp, NULL);
        while (spte) {
            BUG_ON(!spte);
            BUG_ON(!(*spte&  PT_PRESENT_MASK));
BUG_ON((*spte& (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK)) != (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK)); pgprintk("rmap_write_protect(large): spte %p %llx %lld\n", spte, *spte, gfn);
            if (is_writable_pte(*spte)) {
                drop_spte(kvm, spte,
                      shadow_trap_nonpresent_pte);
                --kvm->stat.lpages;
                spte = NULL;
                write_protected = 1;
            }
            spte = rmap_next(kvm, rmapp, spte);
        }
    }
===

Shouldn't be any. I forgot to rmap_remove() and to update kvm_stat, thanks for pointing it out.

I'll post an updated patch. We'll want to share code between the two later on.


Actually, drop_spte() calls rmap_remove(), so all that's broken is kvm->stat.lpages accounting.

--
error compiling committee.c: too many arguments to function

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