After commit b3356bf0dbb349 (KVM: emulator: optimize "rep ins" handling),
the pieces of io data can be collected and write them to the guest memory
or MMIO together.
Unfortunately, kvm splits the mmio access into 8 bytes and store them to
vcpu->mmio_fragments. If the guest uses "rep ins" to move large data, it
will cause vcpu->mmio_fragments overflow
The bug can be exposed by isapc (-M isapc):
[23154.818733] general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC
[ ......]
[23154.858083] Call Trace:
[23154.859874] [<ffffffffa04f0e17>] kvm_get_cr8+0x1d/0x28 [kvm]
[23154.861677] [<ffffffffa04fa6d4>] kvm_arch_vcpu_ioctl_run+0xcda/0xe45 [kvm]
[23154.863604] [<ffffffffa04f5a1a>] ? kvm_arch_vcpu_load+0x17b/0x180 [kvm]
Actually, we can use one mmio_fragment to store a large mmio access for the
mmio access is always continuous then split it when we pass the mmio-exit-info
to userspace. After that, we only need two entries to store mmio info for
the cross-mmio pages access
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 127 +++++++++++++++++++++++++++++-----------------
include/linux/kvm_host.h | 16 +-----
2 files changed, 84 insertions(+), 59 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8b90dd5..41ceb51 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3779,9 +3779,6 @@ static int read_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa,
static int write_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa,
void *val, int bytes)
{
- struct kvm_mmio_fragment *frag = &vcpu->mmio_fragments[0];
-
- memcpy(vcpu->run->mmio.data, frag->data, frag->len);
return X86EMUL_CONTINUE;
}
@@ -3799,6 +3796,64 @@ static const struct read_write_emulator_ops write_emultor = {
.write = true,
};
+static bool get_current_mmio_info(struct kvm_vcpu *vcpu, gpa_t *gpa,
+ unsigned *len, void **data)
+{
+ struct kvm_mmio_fragment *frag;
+ int cur = vcpu->mmio_cur_fragment;
+
+ if (cur >= vcpu->mmio_nr_fragments)
+ return false;
+
+ frag = &vcpu->mmio_fragments[cur];
+ if (frag->pos >= frag->len) {
+ if (++vcpu->mmio_cur_fragment >= vcpu->mmio_nr_fragments)
+ return false;
+ frag++;
+ }
+
+ *gpa = frag->gpa + frag->pos;
+ *data = frag->data + frag->pos;
+ *len = min(8u, frag->len - frag->pos);
+ return true;
+}
+
+static void complete_current_mmio(struct kvm_vcpu *vcpu)
+{
+ struct kvm_mmio_fragment *frag;
+ gpa_t gpa;
+ unsigned len;
+ void *data;
+
+ get_current_mmio_info(vcpu, &gpa, &len, &data);
+
+ if (!vcpu->mmio_is_write)
+ memcpy(data, vcpu->run->mmio.data, len);
+
+ /* Increase frag->pos to switch to the next mmio. */
+ frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment];
+ frag->pos += len;
+}
+
+static bool vcpu_fill_mmio_exit_info(struct kvm_vcpu *vcpu)
+{
+ gpa_t gpa;
+ unsigned len;
+ void *data;
+
+ if (!get_current_mmio_info(vcpu, &gpa, &len, &data))
+ return false;
+
+ vcpu->run->mmio.len = len;
+ vcpu->run->mmio.is_write = vcpu->mmio_is_write;
+ vcpu->run->exit_reason = KVM_EXIT_MMIO;
+ vcpu->run->mmio.phys_addr = gpa;
+
+ if (vcpu->mmio_is_write)
+ memcpy(vcpu->run->mmio.data, data, len);
+ return true;
+}
+
static int emulator_read_write_onepage(unsigned long addr, void *val,
unsigned int bytes,
struct x86_exception *exception,
@@ -3834,18 +3889,12 @@ mmio:
bytes -= handled;
val += handled;
- while (bytes) {
- unsigned now = min(bytes, 8U);
-
- frag = &vcpu->mmio_fragments[vcpu->mmio_nr_fragments++];
- frag->gpa = gpa;
- frag->data = val;
- frag->len = now;
-
- gpa += now;
- val += now;
- bytes -= now;
- }
+ WARN_ON(vcpu->mmio_nr_fragments >= KVM_MAX_MMIO_FRAGMENTS);
+ frag = &vcpu->mmio_fragments[vcpu->mmio_nr_fragments++];
+ frag->pos = 0;
+ frag->gpa = gpa;
+ frag->data = val;
+ frag->len = bytes;
return X86EMUL_CONTINUE;
}
@@ -3855,7 +3904,6 @@ int emulator_read_write(struct x86_emulate_ctxt *ctxt, unsigned long addr,
const struct read_write_emulator_ops *ops)
{
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
- gpa_t gpa;
int rc;
if (ops->read_write_prepare &&
@@ -3887,17 +3935,13 @@ int emulator_read_write(struct x86_emulate_ctxt *ctxt, unsigned long addr,
if (!vcpu->mmio_nr_fragments)
return rc;
- gpa = vcpu->mmio_fragments[0].gpa;
-
vcpu->mmio_needed = 1;
vcpu->mmio_cur_fragment = 0;
+ vcpu->mmio_is_write = ops->write;
- vcpu->run->mmio.len = vcpu->mmio_fragments[0].len;
- vcpu->run->mmio.is_write = vcpu->mmio_is_write = ops->write;
- vcpu->run->exit_reason = KVM_EXIT_MMIO;
- vcpu->run->mmio.phys_addr = gpa;
-
- return ops->read_write_exit_mmio(vcpu, gpa, val, bytes);
+ vcpu_fill_mmio_exit_info(vcpu);
+ return ops->read_write_exit_mmio(vcpu, vcpu->mmio_fragments[0].gpa,
+ val, bytes);
}
static int emulator_read_emulated(struct x86_emulate_ctxt *ctxt,
@@ -5524,43 +5568,34 @@ static int complete_emulated_pio(struct kvm_vcpu *vcpu)
*
* read:
* for each fragment
- * write gpa, len
- * exit
- * copy data
+ * for each mmio piece in the fragment
+ * write gpa, len
+ * exit
+ * copy data
* execute insn
*
* write:
* for each fragment
- * write gpa, len
- * copy data
- * exit
+ * for each mmio piece in the fragment
+ * write gpa, len
+ * copy data
+ * exit
*/
static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
{
- struct kvm_run *run = vcpu->run;
- struct kvm_mmio_fragment *frag;
-
BUG_ON(!vcpu->mmio_needed);
- /* Complete previous fragment */
- frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment++];
- if (!vcpu->mmio_is_write)
- memcpy(frag->data, run->mmio.data, frag->len);
- if (vcpu->mmio_cur_fragment == vcpu->mmio_nr_fragments) {
+ complete_current_mmio(vcpu);
+
+ /* Initiate next fragment */
+ if (!vcpu_fill_mmio_exit_info(vcpu)) {
vcpu->mmio_needed = 0;
if (vcpu->mmio_is_write)
return 1;
vcpu->mmio_read_completed = 1;
return complete_emulated_io(vcpu);
}
- /* Initiate next fragment */
- ++frag;
- run->exit_reason = KVM_EXIT_MMIO;
- run->mmio.phys_addr = frag->gpa;
- if (vcpu->mmio_is_write)
- memcpy(run->mmio.data, frag->data, frag->len);
- run->mmio.len = frag->len;
- run->mmio.is_write = vcpu->mmio_is_write;
+
vcpu->arch.complete_userspace_io = complete_emulated_mmio;
return 0;
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e235068..f6c3c2f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -42,19 +42,8 @@
*/
#define KVM_MEMSLOT_INVALID (1UL << 16)
-/*
- * If we support unaligned MMIO, at most one fragment will be split into two:
- */
-#ifdef KVM_UNALIGNED_MMIO
-# define KVM_EXTRA_MMIO_FRAGMENTS 1
-#else
-# define KVM_EXTRA_MMIO_FRAGMENTS 0
-#endif
-
-#define KVM_USER_MMIO_SIZE 8
-
-#define KVM_MAX_MMIO_FRAGMENTS \
- (KVM_MMIO_SIZE / KVM_USER_MMIO_SIZE + KVM_EXTRA_MMIO_FRAGMENTS)
+/* Two fragments for cross MMIO pages. */
+#define KVM_MAX_MMIO_FRAGMENTS 2
/*
* For the normal pfn, the highest 12 bits should be zero,
@@ -203,6 +192,7 @@ struct kvm_mmio_fragment {
gpa_t gpa;
void *data;
unsigned len;
+ unsigned pos;
};
struct kvm_vcpu {
--
1.7.7.6
--
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