On 2011-04-21 17:34, Takuya Yoshikawa wrote:
> From: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
>
> This patch optimizes the guest page table walk by using get_user()
> instead of copy_from_user().
>
> With this patch applied, paging64_walk_addr_generic() has become
> about 0.5us to 1.0us faster on my Phenom II machine with NPT on.
>
> Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
> ---
> arch/x86/kvm/paging_tmpl.h | 23 ++++++++++++++++++++---
> 1 files changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 74f8567..825d953 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -117,6 +117,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
> gva_t addr, u32 access)
> {
> pt_element_t pte;
> + pt_element_t __user *ptep_user;
> gfn_t table_gfn;
> unsigned index, pt_access, uninitialized_var(pte_access);
> gpa_t pte_gpa;
> @@ -152,6 +153,9 @@ walk:
> pt_access = ACC_ALL;
>
> for (;;) {
> + gfn_t real_gfn;
> + unsigned long host_addr;
> +
> index = PT_INDEX(addr, walker->level);
>
> table_gfn = gpte_to_gfn(pte);
> @@ -160,9 +164,22 @@ walk:
> walker->table_gfn[walker->level - 1] = table_gfn;
> walker->pte_gpa[walker->level - 1] = pte_gpa;
>
> - if (kvm_read_guest_page_mmu(vcpu, mmu, table_gfn, &pte,
> - offset, sizeof(pte),
> - PFERR_USER_MASK|PFERR_WRITE_MASK)) {
> + real_gfn = mmu->translate_gpa(vcpu, gfn_to_gpa(table_gfn),
> + PFERR_USER_MASK|PFERR_WRITE_MASK);
> + if (real_gfn == UNMAPPED_GVA) {
> + present = false;
> + break;
> + }
> + real_gfn = gpa_to_gfn(real_gfn);
> +
> + host_addr = gfn_to_hva(vcpu->kvm, real_gfn);
> + if (kvm_is_error_hva(host_addr)) {
> + present = false;
> + break;
> + }
> +
> + ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
> + if (get_user(pte, ptep_user)) {
^^^^^^^^^^^^
This doesn't work for x86-32: pte is 64 bit, but get_user is only
defined up to 32 bit on that platform.
Avi, what's your 32-bit buildbot doing? :)
Jan
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