From: Takuya Yoshikawa <yoshikawa.tak...@oss.ntt.co.jp>
We optimize multi level guest page table walk as follows:
1. We cache the memslot which, probably, includes the next guest page
tables to avoid searching for it many times.
2. We use get_user() instead of copy_from_user().
Note that this is kind of a restricted way of Xiao's more generic
work: "KVM: optimize memslots searching and cache GPN to GFN."
With this patch applied, paging64_walk_addr_generic() has improved
as the following tracing results show.
Before:
3.169 us | paging64_walk_addr_generic();
1.880 us | paging64_walk_addr_generic();
1.243 us | paging64_walk_addr_generic();
1.517 us | paging64_walk_addr_generic();
3.009 us | paging64_walk_addr_generic();
1.814 us | paging64_walk_addr_generic();
1.340 us | paging64_walk_addr_generic();
1.659 us | paging64_walk_addr_generic();
1.748 us | paging64_walk_addr_generic();
1.488 us | paging64_walk_addr_generic();
After:
1.714 us | paging64_walk_addr_generic();
0.806 us | paging64_walk_addr_generic();
0.664 us | paging64_walk_addr_generic();
0.619 us | paging64_walk_addr_generic();
0.645 us | paging64_walk_addr_generic();
0.605 us | paging64_walk_addr_generic();
1.388 us | paging64_walk_addr_generic();
0.753 us | paging64_walk_addr_generic();
0.594 us | paging64_walk_addr_generic();
0.833 us | paging64_walk_addr_generic();
Signed-off-by: Takuya Yoshikawa <yoshikawa.tak...@oss.ntt.co.jp>
---
arch/x86/kvm/paging_tmpl.h | 37 ++++++++++++++++++++++++++++++++-----
1 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 109939a..614aa3f 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -109,12 +109,37 @@ static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu,
pt_element_t gpte)
return access;
}
+/*
+ * Read the guest PTE refered to by table_gfn and offset and put it into ptep.
+ *
+ * *slot_hint, if not NULL, should point to a memslot which probably includes
+ * the guest PTE. The actual memslot will be put back into this so that
+ * callers can cache it.
+ */
static int FNAME(read_guest_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
- gfn_t table_gfn, int offset, pt_element_t
*ptep)
+ gfn_t table_gfn, int offset, pt_element_t
*ptep,
+ struct kvm_memory_slot **slot_hint)
{
- return kvm_read_guest_page_mmu(vcpu, mmu, table_gfn, ptep,
- offset, sizeof(*ptep),
- PFERR_USER_MASK | PFERR_WRITE_MASK);
+ unsigned long addr;
+ pt_element_t __user *ptep_user;
+ gfn_t real_gfn;
+
+ real_gfn = mmu->translate_gpa(vcpu, gfn_to_gpa(table_gfn),
+ PFERR_USER_MASK | PFERR_WRITE_MASK);
+ if (real_gfn == UNMAPPED_GVA)
+ return -EFAULT;
+
+ real_gfn = gpa_to_gfn(real_gfn);
+
+ if (!(*slot_hint) || !gfn_in_memslot(*slot_hint, real_gfn))
+ *slot_hint = gfn_to_memslot(vcpu->kvm, real_gfn);
+
+ addr = gfn_to_hva_memslot(*slot_hint, real_gfn);
+ if (kvm_is_error_hva(addr))
+ return -EFAULT;
+
+ ptep_user = (pt_element_t __user *)((void *)addr + offset);
+ return get_user(*ptep, ptep_user);
}
/*
@@ -130,6 +155,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker
*walker,
gpa_t pte_gpa;
bool eperm, present, rsvd_fault;
int offset, write_fault, user_fault, fetch_fault;
+ struct kvm_memory_slot *slot_cache = NULL;
write_fault = access & PFERR_WRITE_MASK;
user_fault = access & PFERR_USER_MASK;
@@ -168,7 +194,8 @@ walk:
walker->table_gfn[walker->level - 1] = table_gfn;
walker->pte_gpa[walker->level - 1] = pte_gpa;
- if (FNAME(read_guest_pte)(vcpu, mmu, table_gfn, offset, &pte)) {
+ if (FNAME(read_guest_pte)(vcpu, mmu, table_gfn,
+ offset, &pte, &slot_cache)) {
present = false;
break;
}
--
1.7.1
--
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