[PATCH 03/12] arm: KVM: force execution of HCPTR access on VM exit
marc.zyngier at arm.com
Fri Jun 19 05:53:07 PDT 2015
On VM entry, we disable access to the VFP registers in order to
perform a lazy save/restore of these registers.
On VM exit, we restore access, test if we did enable them before,
and save/restore the guest/host registers if necessary. In this
sequence, the FPEXC register is always accessed, irrespective
of the trapping configuration.
If the guest didn't touch the VFP registers, then the HCPTR access
has now enabled such access, but we're missing a barrier to ensure
architectural execution of the new HCPTR configuration. If the HCPTR
access has been delayed/reordered, the subsequent access to FPEXC
will cause a trap, which we aren't prepared to handle at all.
The same condition exists when trapping to enable VFP for the guest.
The fix is to introduce a barrier after enabling VFP access. In the
vmexit case, it can be relaxed to only takes place if the guest hasn't
accessed its view of the VFP registers, making the access to FPEXC safe.
The set_hcptr macro is modified to deal with both vmenter/vmexit and
vmtrap operations, and now takes an optional label that is branched to
when the guest hasn't touched the VFP registers.
Reported-by: Vikram Sethi <vikrams at codeaurora.org>
Cc: stable at kernel.org # v3.9+
Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
arch/arm/kvm/interrupts.S | 10 ++++------
arch/arm/kvm/interrupts_head.S | 20 ++++++++++++++++++--
2 files changed, 22 insertions(+), 8 deletions(-)
diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
index 79caf79..f7db3a5 100644
@@ -170,13 +170,9 @@ __kvm_vcpu_return:
@ Don't trap coprocessor accesses for host kernel
- set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
+ set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)), after_vfp_restore
- @ Save floating point registers we if let guest use them.
- tst r2, #(HCPTR_TCP(10) | HCPTR_TCP(11))
- bne after_vfp_restore
@ Switch VFP/NEON hardware state to the host's
add r7, vcpu, #VCPU_VFP_GUEST
@@ -188,6 +184,8 @@ after_vfp_restore:
@ Restore FPEXC_EN which we clobbered on entry
VFPFMXR FPEXC, r2
@ Reset Hyp-role
@@ -483,7 +481,7 @@ switch_to_guest_vfp:
@ NEON/VFP used. Turn on VFP access.
- set_hcptr vmexit, (HCPTR_TCP(10) | HCPTR_TCP(11))
+ set_hcptr vmtrap, (HCPTR_TCP(10) | HCPTR_TCP(11))
@ Switch VFP/NEON hardware state to the guest's
add r7, r0, #VCPU_VFP_HOST
diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
index 35e4a3a..48efe2e 100644
@@ -591,8 +591,13 @@ ARM_BE8(rev r6, r6 )
/* Configures the HCPTR (Hyp Coprocessor Trap Register) on entry/return
- * (hardware reset value is 0). Keep previous value in r2. */
-.macro set_hcptr operation, mask
+ * (hardware reset value is 0). Keep previous value in r2.
+ * An ISB is emited on vmexit/vmtrap, but executed on vmexit only if
+ * VFP wasn't already enabled (always executed on vmtrap).
+ * If a label is specified with vmexit, it is branched to if VFP wasn't
+ * enabled.
+.macro set_hcptr operation, mask, label = none
mrc p15, 4, r2, c1, c1, 2
ldr r3, =\mask
.if \operation == vmentry
@@ -601,6 +606,17 @@ ARM_BE8(rev r6, r6 )
bic r3, r2, r3 @ Don't trap defined coproc-accesses
mcr p15, 4, r3, c1, c1, 2
+ .if \operation != vmentry
+ .if \operation == vmexit
+ tst r2, #(HCPTR_TCP(10) | HCPTR_TCP(11))
+ beq 1f
+ .if \label != none
+ b \label
/* Configures the HDCR (Hyp Debug Configuration Register) on entry/return
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