On 04/18/2011 09:38 PM, Takuya Yoshikawa wrote:
From: Takuya Yoshikawa<yoshikawa.takuya@xxxxxxxxxxxxx>
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."
Good optimization. copy_from_user() really isn't optimized for short
buffers, I expect much of the improvement comes from that.
+/*
+ * 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.
+ */
Please drop the slot_hint optimization. First, it belongs in a separate
patch. Second, I prefer to see a generic slot sort instead of an ad-hoc
cache.
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;
}
--
error compiling committee.c: too many arguments to function
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