2023-01-27 11:31:54

by Anup Patel

Subject: [PATCH v2] RISC-V: KVM: Redirect illegal instruction traps to guest

From: Andy Chiu <[email protected]>

The M-mode redirects an unhandled illegal instruction trap back
to S-mode. However, KVM running in HS-mode terminates the VS-mode
software when it receives illegal instruction trap. Instead, KVM
should redirect the illegal instruction trap back to VS-mode, and
let VS-mode trap handler decide the next step. This futher allows
guest kernel to implement on-demand enabling of vector extension
for a guest user space process upon first-use.

Signed-off-by: Andy Chiu <[email protected]>
Signed-off-by: Anup Patel <[email protected]>
---
arch/riscv/kvm/vcpu_exit.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
index c9f741ab26f5..4ea101a73d8b 100644
--- a/arch/riscv/kvm/vcpu_exit.c
+++ b/arch/riscv/kvm/vcpu_exit.c
@@ -160,6 +160,9 @@ void kvm_riscv_vcpu_trap_redirect(struct kvm_vcpu *vcpu,

/* Set Guest PC to Guest exception vector */
vcpu->arch.guest_context.sepc = csr_read(CSR_VSTVEC);
+
+ /* Set Guest privilege mode to supervisor */
+ vcpu->arch.guest_context.sstatus |= SR_SPP;
}

/*
@@ -179,6 +182,12 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
ret = -EFAULT;
run->exit_reason = KVM_EXIT_UNKNOWN;
switch (trap->scause) {
+ case EXC_INST_ILLEGAL:
+ if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV) {
+ kvm_riscv_vcpu_trap_redirect(vcpu, trap);
+ ret = 1;
+ }
+ break;
case EXC_VIRTUAL_INST_FAULT:
if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV)
ret = kvm_riscv_vcpu_virtual_insn(vcpu, run, trap);
--
2.34.1

2023-01-27 12:12:36

by Andrew Jones

Subject: Re: [PATCH v2] RISC-V: KVM: Redirect illegal instruction traps to guest

On Fri, Jan 27, 2023 at 04:59:34PM +0530, Anup Patel wrote:
> From: Andy Chiu <[email protected]>
>
> The M-mode redirects an unhandled illegal instruction trap back
> to S-mode. However, KVM running in HS-mode terminates the VS-mode
> software when it receives illegal instruction trap. Instead, KVM
> should redirect the illegal instruction trap back to VS-mode, and
> let VS-mode trap handler decide the next step. This futher allows
> guest kernel to implement on-demand enabling of vector extension
> for a guest user space process upon first-use.
>
> Signed-off-by: Andy Chiu <[email protected]>
> Signed-off-by: Anup Patel <[email protected]>
> ---
> arch/riscv/kvm/vcpu_exit.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
> index c9f741ab26f5..4ea101a73d8b 100644
> --- a/arch/riscv/kvm/vcpu_exit.c
> +++ b/arch/riscv/kvm/vcpu_exit.c
> @@ -160,6 +160,9 @@ void kvm_riscv_vcpu_trap_redirect(struct kvm_vcpu *vcpu,
>
> /* Set Guest PC to Guest exception vector */
> vcpu->arch.guest_context.sepc = csr_read(CSR_VSTVEC);
> +
> + /* Set Guest privilege mode to supervisor */
> + vcpu->arch.guest_context.sstatus |= SR_SPP;

This could/should be a separate fix patch, right?

> }
>
> /*
> @@ -179,6 +182,12 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
> ret = -EFAULT;
> run->exit_reason = KVM_EXIT_UNKNOWN;
> switch (trap->scause) {
> + case EXC_INST_ILLEGAL:
> + if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV) {
> + kvm_riscv_vcpu_trap_redirect(vcpu, trap);
> + ret = 1;
> + }
> + break;
> case EXC_VIRTUAL_INST_FAULT:
> if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV)
> ret = kvm_riscv_vcpu_virtual_insn(vcpu, run, trap);
> --
> 2.34.1
>

Otherwise,

Reviewed-by: Andrew Jones <[email protected]>

Thanks,
drew