Re: [PATCH v5 10/20] RISC-V: KVM: Handle MMIO exits for VCPU

[Andrew Jones]

On Thu, Aug 22, 2019 at 02:10:48PM +0200, Alexander Graf wrote:
> On 22.08.19 10:44, Anup Patel wrote:
...
> > +static int emulate_load(struct kvm_vcpu *vcpu, struct kvm_run *run,
> > +			unsigned long fault_addr)
...
> > +	/* Exit to userspace for MMIO emulation */
> > +	vcpu->stat.mmio_exit_user++;
> > +	run->exit_reason = KVM_EXIT_MMIO;
> > +	run->mmio.is_write = false;
> > +	run->mmio.phys_addr = fault_addr;
> > +	run->mmio.len = len;
> > +
> > +	/* Move to next instruction */
> > +	vcpu->arch.guest_context.sepc += INSN_LEN(insn);
> 
> Doesn't that make more sense on the reentry path? What if you want to inject
> an MCE on access to unmapped addresses from user space?
>

I agree. See commit 0d640732dbeb for arm's justification for moving
the instruction skip. But also see

https://patchwork.kernel.org/patch/11109063/

for a needed fix to avoid skipping the instructions multiple times.
It looks like riscv's KVM_RUN ioctl would be vulnerable to that as
well.

Thanks,
drew