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 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 | 60 ++++++++++++++++++++++++++--------------------
include/linux/kvm_host.h | 15 +----------
2 files changed, 36 insertions(+), 39 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8b90dd5..ec07cd3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3781,7 +3781,7 @@ static int write_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa,
{
struct kvm_mmio_fragment *frag = &vcpu->mmio_fragments[0];
- memcpy(vcpu->run->mmio.data, frag->data, frag->len);
+ memcpy(vcpu->run->mmio.data, frag->data, min(8u, frag->len));
return X86EMUL_CONTINUE;
}
@@ -3834,18 +3834,11 @@ 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->gpa = gpa;
+ frag->data = val;
+ frag->len = bytes;
return X86EMUL_CONTINUE;
}
@@ -3892,7 +3885,7 @@ int emulator_read_write(struct x86_emulate_ctxt *ctxt, unsigned long addr,
vcpu->mmio_needed = 1;
vcpu->mmio_cur_fragment = 0;
- vcpu->run->mmio.len = vcpu->mmio_fragments[0].len;
+ vcpu->run->mmio.len = min(8u, 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;
@@ -5524,28 +5517,44 @@ 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;
+ unsigned len;
BUG_ON(!vcpu->mmio_needed);
/* Complete previous fragment */
- frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment++];
+ frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment];
+ len = min(8u, frag->len);
if (!vcpu->mmio_is_write)
- memcpy(frag->data, run->mmio.data, frag->len);
+ memcpy(frag->data, run->mmio.data, len);
+
+ if (frag->len <= 8) {
+ /* Switch to the next fragment. */
+ frag++;
+ vcpu->mmio_cur_fragment++;
+ } else {
+ /* Go forward to the next mmio piece. */
+ frag->data += len;
+ frag->gpa += len;
+ frag->len -= len;
+ }
+
if (vcpu->mmio_cur_fragment == vcpu->mmio_nr_fragments) {
vcpu->mmio_needed = 0;
if (vcpu->mmio_is_write)
@@ -5553,13 +5562,12 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
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;
+ memcpy(run->mmio.data, frag->data, min(8u, frag->len));
+ run->mmio.len = min(8u, 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..a92f4fd 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,
--
1.7.7.6
--
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