Re: [PATCH] KVM: dirty all pages in kvm_write_guest_cached()

Paolo Bonzini
2015-04-08T08:49:59Z

On 07/04/2015 22:34, Radim Krčmář wrote:
> We dirtied only one page because writes originally couldn't span more.
> Use improved syntax for '>> PAGE_SHIFT' while at it.
>
> Fixes: 8f964525a121 ("KVM: Allow cross page reads and writes from cached translations.")
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

Cross-page reads and writes should never get here; they have
ghc->memslot set to NULL and go through the slow path in kvm_write_guest.

What am I missing?

Paolo

> ---
> The function handles cross memslot writes in a different path.
>
> I think we should dirty pages after partial writes too (r < len),
> but it probably won't happen and I already started refactoring :)
>
> virt/kvm/kvm_main.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index aadef264bed1..863df9dcab6f 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1665,6 +1665,7 @@ int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> {
> struct kvm_memslots *slots = kvm_memslots(kvm);
> int r;
> + gfn_t gfn;
>
> BUG_ON(len > ghc->len);
>
> @@ -1680,7 +1681,10 @@ int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> r = __copy_to_user((void __user *)ghc->hva, data, len);
> if (r)
> return -EFAULT;
> - mark_page_dirty_in_slot(kvm, ghc->memslot, ghc->gpa >> PAGE_SHIFT);
> +
> + for (gfn = gpa_to_gfn(ghc->gpa);
> + gfn <= gpa_to_gfn(ghc->gpa + len - 1); gfn++)
> + mark_page_dirty_in_slot(kvm, ghc->memslot, gfn);
>
> return 0;
> }
>