On Sun, May 01, 2011 at 02:33:07PM +0900, Takuya Yoshikawa wrote:
> From: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
>
> The address of the gpte was already calculated and stored in ptep_user
> before entering cmpxchg_gpte().
>
> This patch makes cmpxchg_gpte() to use that to make it clear that we
> are using the same address during walk_addr_generic().
>
> Note that the unlikely annotations are used to show that the conditions
> are something unusual rather than for performance.
>
> Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
> ---
> arch/x86/kvm/paging_tmpl.h | 26 ++++++++++++--------------
> 1 files changed, 12 insertions(+), 14 deletions(-)
Hi Takuya,
>
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 52450a6..f9d9af1 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -79,21 +79,19 @@ static gfn_t gpte_to_gfn_lvl(pt_element_t gpte, int lvl)
> }
>
> static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> - gfn_t table_gfn, unsigned index,
> - pt_element_t orig_pte, pt_element_t new_pte)
> + pt_element_t __user *ptep_user, unsigned index,
> + pt_element_t orig_pte, pt_element_t new_pte)
> {
> + int npages;
> pt_element_t ret;
> pt_element_t *table;
> struct page *page;
> - gpa_t gpa;
>
> - gpa = mmu->translate_gpa(vcpu, table_gfn << PAGE_SHIFT,
> - PFERR_USER_MASK|PFERR_WRITE_MASK);
> - if (gpa == UNMAPPED_GVA)
> + npages = get_user_pages_fast((unsigned long)ptep_user, 1, 1, &page);
> + /* Check if the user is doing something meaningless. */
> + if (unlikely(npages != 1))
> return -EFAULT;
>
> - page = gfn_to_page(vcpu->kvm, gpa_to_gfn(gpa));
> -
gfn_to_page is the interface for mapping guest pages inside KVM,
and you're bypassing it for IMO no good reason (i doubt there's any
performance improvement by skipping the translation).
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