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KVM: MMU: Optimize guest page table walk 

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@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Takuya Yoshikawa 2011-04-22 00:34:44 +09:00 committed by Avi Kivity
parent 40e19b519c
commit 6e2ca7d180
1 changed files with 20 additions and 3 deletions
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23
arch/x86/kvm/paging_tmpl.h
View File

@ -123,6 +123,7 @@ 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;
@ -158,6 +159,9 @@ 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);
@ -166,9 +170,22 @@ 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)) {
present = false;
break;
}