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MIPS: KVM/locore.S: Don't preserve host ASID around vcpu_run

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MIPS KVM uses different ASIDs for guest execution than for the host.
The host ASID is saved on the stack when entering the guest with
__kvm_mips_vcpu_run(), and restored again before returning back to the
caller (exit to userland).

- This does not take into account that pre-emption may have taken place
  during that time, which may have started a new ASID cycle and resulted
  in that process' ASID being invalidated and reused.

- This does not take into account that the process may have migrated to
  a different CPU during that time, with a different ASID assignment
  since they are managed per-CPU.

- It is actually redundant, since the host ASID will be restored
  correctly by kvm_arch_vcpu_put(), which is called almost immediately
  after kvm_arch_vcpu_ioctl_run() returns.

Therefore drop this code from locore.S

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13206/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
James Hogan 2016-05-06 14:36:18 +01:00 committed by Ralf Baechle
parent 97b921087f
commit 5fb59fd2e7
1 changed files with 0 additions and 12 deletions
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12
arch/mips/kvm/locore.S
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@ -32,7 +32,6 @@
EXPORT(x);
/* Overload, Danger Will Robinson!! */
#define PT_HOST_ASID PT_BVADDR
#define PT_HOST_USERLOCAL PT_EPC
#define CP0_DDATA_LO $28,3
@ -104,11 +103,6 @@ FEXPORT(__kvm_mips_vcpu_run)
mfc0 v0, CP0_STATUS
LONG_S v0, PT_STATUS(k1)
/* Save host ASID, shove it into the BVADDR location */
mfc0 v1, CP0_ENTRYHI
andi v1, 0xff
LONG_S v1, PT_HOST_ASID(k1)
/* Save DDATA_LO, will be used to store pointer to vcpu */
mfc0 v1, CP0_DDATA_LO
LONG_S v1, PT_HOST_USERLOCAL(k1)
@ -551,12 +545,6 @@ __kvm_mips_return_to_host:
LONG_L k0, PT_HOST_USERLOCAL(k1)
mtc0 k0, CP0_DDATA_LO
/* Restore host ASID */
LONG_L k0, PT_HOST_ASID(sp)
andi k0, 0xff
mtc0 k0,CP0_ENTRYHI
ehb
/* Load context saved on the host stack */
LONG_L $0, PT_R0(k1)
LONG_L $1, PT_R1(k1)