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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
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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,