From: Avi Kivity <avi@redhat.com>
Date: Wed, 1 Aug 2012 13:48:03 +0000 (+0300)
Subject: KVM: VMX: Fix ds/es corruption on i386 with preemption
X-Git-Tag: v3.6-rc2~33^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=aa67f6096c19bcdb1951ef88be3cf3d2118809dc;p=pandora-kernel.git

KVM: VMX: Fix ds/es corruption on i386 with preemption

Commit b2da15ac26a0c ("KVM: VMX: Optimize %ds, %es reload") broke i386
in the following scenario:

  vcpu_load
  ...
  vmx_save_host_state
  vmx_vcpu_run
  (ds.rpl, es.rpl cleared by hardware)

  interrupt
    push ds, es  # pushes bad ds, es
    schedule
      vmx_vcpu_put
        vmx_load_host_state
          reload ds, es (with __USER_DS)
    pop ds, es  # of other thread's stack
    iret
  # other thread runs
  interrupt
    push ds, es
    schedule  # back in vcpu thread
    pop ds, es  # now with rpl=0
    iret
  ...
  vcpu_put
  resume_userspace
  iret  # clears ds, es due to mismatched rpl

(instead of resume_userspace, we might return with SYSEXIT and then
take an exception; when the exception IRETs we end up with cleared
ds, es)

Fix by avoiding the optimization on i386 and reloading ds, es on the
lightweight exit path.

Reported-by: Chris Clayron <chris2553@googlemail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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