On 04/30/2015 02:36 PM, Paolo Bonzini wrote:
This adds an arch-specific memslot flag that hides slots unless the
VCPU is in system management mode.
Some care is needed in order to limit the overhead of x86_gfn_to_memslot
when compared with gfn_to_memslot. Thankfully, we have __gfn_to_memslot
and search_memslots which are the same, so we can add some extra output
to search_memslots. The compiler will optimize it as dead code in
__gfn_to_memslot, and will use it to thread jumps in x86_gfn_to_memslot.
struct kvm_memory_slot *x86_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn)
{
- struct kvm_memory_slot *slot = gfn_to_memslot(vcpu->kvm, gfn);
+ /* By using search_memslots directly the compiler can optimize away
+ * the "if (found)" check below.
+ *
+ * It cannot do the same for gfn_to_memslot because it is not inlined,
+ * and it also cannot do the same for __gfn_to_memslot because the
+ * kernel is compiled with -fno-delete-null-pointer-checks.
+ */
+ bool found;
+ struct kvm_memslots *memslots = kvm_memslots(vcpu->kvm);
+ struct kvm_memory_slot *slot = search_memslots(memslots, gfn, &found);
+
+ if (found && unlikely(slot->flags & KVM_MEM_X86_SMRAM) && !is_smm(vcpu))
+ return NULL;
Alternative approach: store the memslot pointer in the vcpu, instead of
of vcpu->kvm. The uapi interface code can generate two memslot tables
to be stored in kvm->, one for smm and one for !smm.
This is a little more generic and can be used for other asymmetric
memory maps causes (the only one I can think of, mapping the APIC to
different physical addresses, can't be efficiently supported).
return slot;
}
@@ -112,7 +125,15 @@ EXPORT_SYMBOL_GPL(x86_read_guest);
int x86_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
gpa_t gpa, unsigned long len)
{
- return kvm_gfn_to_hva_cache_init(kvm, ghc, gpa, len);
+ int r = kvm_gfn_to_hva_cache_init(kvm, ghc, gpa, len);
+
+ if (r < 0)
+ return r;
+
+ /* Use slow path for reads and writes to SMRAM. */
+ if (ghc->memslot && (ghc->memslot->flags & KVM_MEM_X86_SMRAM))
+ ghc->memslot = NULL;
+ return r;
}
EXPORT_SYMBOL_GPL(x86_gfn_to_hva_cache_init);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e7cfee09970a..ea3db5d89f67 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -800,16 +800,18 @@ static inline void kvm_guest_exit(void)
* gfn_to_memslot() itself isn't here as an inline because that would
* bloat other code too much.
*/
-static inline struct kvm_memory_slot *
-search_memslots(struct kvm_memslots *slots, gfn_t gfn)
+static __always_inline struct kvm_memory_slot *
+search_memslots(struct kvm_memslots *slots, gfn_t gfn, bool *found)
{
int start = 0, end = slots->used_slots;
int slot = atomic_read(&slots->lru_slot);
struct kvm_memory_slot *memslots = slots->memslots;
if (gfn >= memslots[slot].base_gfn &&
- gfn < memslots[slot].base_gfn + memslots[slot].npages)
+ gfn < memslots[slot].base_gfn + memslots[slot].npages) {
+ *found = true;
return &memslots[slot];
+ }
while (start < end) {
slot = start + (end - start) / 2;
@@ -823,16 +825,20 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn)
if (gfn >= memslots[start].base_gfn &&
gfn < memslots[start].base_gfn + memslots[start].npages) {
atomic_set(&slots->lru_slot, start);
+ *found = true;
return &memslots[start];
}
+ *found = false;
return NULL;
}
static inline struct kvm_memory_slot *
__gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
{
- return search_memslots(slots, gfn);
+ bool found;
+
+ return search_memslots(slots, gfn, &found);
}
static inline unsigned long
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e82c46b9860f..b8b76106a003 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -716,6 +716,10 @@ static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
#ifdef __KVM_HAVE_READONLY_MEM
valid_flags |= KVM_MEM_READONLY;
#endif
+#ifdef __KVM_ARCH_VALID_FLAGS
+ BUILD_BUG_ON(__KVM_ARCH_VALID_FLAGS & KVM_MEMSLOT_INVALID);
+ valid_flags |= __KVM_ARCH_VALID_FLAGS;
+#endif
if (mem->flags & ~valid_flags)
return -EINVAL;
--
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