On 2019-12-23 11:56, Andrew Murray wrote:

On Sun, Dec 22, 2019 at 10:42:05AM +0000, Marc Zyngier wrote:

quoted

On Fri, 20 Dec 2019 14:30:18 +0000,
Andrew Murray [off-list ref] wrote:

quoted

As we now save/restore the profiler state there is no need to trap
accesses to the statistical profiling controls. Let's unset the
_TPMS bit.

Signed-off-by: Andrew Murray <redacted>
---
 arch/arm64/kvm/debug.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 43487f035385..07ca783e7d9e 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c

@@ -88,7 +88,6 @@ void kvm_arm_reset_debug_ptr(struct kvm_vcpu 

*vcpu)

quoted

  *  - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
  *  - Debug ROM Address (MDCR_EL2_TDRA)
  *  - OS related registers (MDCR_EL2_TDOSA)
- *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
  *
  * Additionally, KVM only traps guest accesses to the debug 

registers if

quoted

  * the guest is not actively using them (see the 

KVM_ARM64_DEBUG_DIRTY

quoted

@@ -111,7 +110,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu 

*vcpu)

quoted

 	 */
 	vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & 

MDCR_EL2_HPMN_MASK;

quoted

 	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
-				MDCR_EL2_TPMS |

No. This is an *optional* feature (the guest could not be presented
with the SPE feature, or the the support simply not be compiled in).

If the guest is not allowed to see the feature, for whichever 
reason,
the traps *must* be enabled and handled.

I'll update this (and similar) to trap such registers when we don't 
support
SPE in the guest.

My original concern in the cover letter was in how to prevent the 
guest
from attempting to use these registers in the first place - I think 
the
solution I was looking for is to trap-and-emulate ID_AA64DFR0_EL1 
such that
the PMSVer bits indicate that SPE is not emulated.

That, and active trapping of the SPE system registers resulting in 
injection
of an UNDEF into the offending guest.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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