• Xiao Guangrong's avatar
    KVM: x86: fix vcpu->mmio_fragments overflow · 87da7e66
    Xiao Guangrong authored
    After commit b3356bf0
     (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: default avatarXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
    Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>