KVM: MMU: flush tlb if the spte can be locklessly modified
authorXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Thu, 17 Apr 2014 09:06:15 +0000 (17:06 +0800)
committerMarcelo Tosatti <mtosatti@redhat.com>
Wed, 23 Apr 2014 20:49:51 +0000 (17:49 -0300)
commit7f31c9595e3c87f68dc54b3269e900f3017ed405
tree8545bf72ce7f938141a4f90c0b8c8fdb7c90c77f
parentc126d94f2c90ed9daee24a94f1c67aff7e9bf387
KVM: MMU: flush tlb if the spte can be locklessly modified

Relax the tlb flush condition since we will write-protect the spte out of mmu
lock. Note lockless write-protection only marks the writable spte to readonly
and the spte can be writable only if both SPTE_HOST_WRITEABLE and
SPTE_MMU_WRITEABLE are set (that are tested by spte_is_locklessly_modifiable)

This patch is used to avoid this kind of race:

      VCPU 0                         VCPU 1
lockless wirte protection:
      set spte.w = 0
                                 lock mmu-lock

                                 write protection the spte to sync shadow page,
                                 see spte.w = 0, then without flush tlb

 unlock mmu-lock

                                 !!! At this point, the shadow page can still be
                                     writable due to the corrupt tlb entry
     Flush all TLB

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
arch/x86/kvm/mmu.c