On 2020-10-26 14:04, Mark Rutland wrote:
On Mon, Oct 26, 2020 at 01:34:42PM +0000, Marc Zyngier wrote:
In an effort to remove the vcpu PC manipulations from EL1 on nVHE
systems, move kvm_skip_instr() to be HYP-specific. EL1's intent
to increment PC post emulation is now signalled via a flag in the
vcpu structure.
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
[...]
+/*
+ * Adjust the guest PC on entry, depending on flags provided by EL1
+ * for the purpose of emulation (MMIO, sysreg).
+ */
+static inline void __adjust_pc(struct kvm_vcpu *vcpu)
+{
+ if (vcpu->arch.flags & KVM_ARM64_INCREMENT_PC) {
+ kvm_skip_instr(vcpu);
+ vcpu->arch.flags &= ~KVM_ARM64_INCREMENT_PC;
+ }
+}
What's your plan for restricting *when* EL1 can ask for the PC to be
adjusted?
I'm assuming that either:
1. You have EL2 sanity-check all responses from EL1 are permitted for
the current state. e.g. if EL1 asks to increment the PC, EL2 must
check that that was a sane response for the current state.
2. You raise the level of abstraction at the EL2/EL1 boundary, such
that
EL2 simply knows. e.g. if emulating a memory access, EL1 can either
provide the response or signal an abort, but doesn't choose to
manipulate the PC as EL2 will infer the right thing to do.
I know that either are tricky in practice, so I'm curious what your
view
is. Generally option #2 is easier to fortify, but I guess we might have
to do #1 since we also have to support unprotected VMs?
To be honest, I'm still in two minds about it, which is why I have
gone with this "middle of the road" option (moving the PC update
to EL2, but leave the control at EL1).
I guess the answer is "it depends". MMIO is easy to put in the #2 model,
while things like WFI/WFE really need #1. sysregs are yet another can of
worm.
M.
--
Jazz is not dead. It just smells funny...
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