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KVM: x86: fix vcpu->mmio_fragments overflow

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After commit b3356bf0db (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@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Xiao Guangrong 2012-10-24 14:07:59 +08:00 committed by Marcelo Tosatti
parent 35fd3dc58d
commit 87da7e66a4
2 changed files with 36 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
arch/x86/kvm/x86.c
View File

@ -3779,7 +3779,7 @@ 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;
}
@ -3832,18 +3832,11 @@ 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;
}
@ -3890,7 +3883,7 @@ 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;
@ -5522,28 +5515,44 @@ 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)
@ -5551,13 +5560,12 @@ 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;

15
include/linux/kvm_host.h
View File

@ -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,