[PATCH] RISC-V:KVM: Add AMO load/store access fault traps to redirect to guest

[PATCH] RISC-V:KVM: Add AMO load/store access fault traps to redirect to guest

[Yu-Wei Hsu]

When unhandled AMO load/store access fault traps are not delegated to
VS mode (hedeleg), M mode redirects them back to S mode.
However, upon returning from M mode,the KVM executed in HS mode terminates
VS mode software.
KVM should redirect traps back to VS mode and let the VS mode trap handler
determine the next steps.
This is one approach to handling access fault traps in KVM,
not only redirecting them to VS mode or terminating it.

Signed-off-by: Yu-Wei Hsu <betterman5240@gmail.com>
---
 arch/riscv/kvm/vcpu_exit.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
index 2415722c01b8..ef8c5e3ec8a0 100644
--- a/arch/riscv/kvm/vcpu_exit.c
+++ b/arch/riscv/kvm/vcpu_exit.c
@@ -185,6 +185,8 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	case EXC_INST_ILLEGAL:
 	case EXC_LOAD_MISALIGNED:
 	case EXC_STORE_MISALIGNED:
+	case EXC_LOAD_ACCESS:
+	case EXC_STORE_ACCESS:
 		if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV) {
 			kvm_riscv_vcpu_trap_redirect(vcpu, trap);
 			ret = 1;
-- 
2.25.1


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Re: [PATCH] RISC-V:KVM: Add AMO load/store access fault traps to redirect to guest

[Anup Patel]

On Mon, Apr 29, 2024 at 2:51 PM Yu-Wei Hsu <betterman5240@gmail.com> wrote:
>
> When unhandled AMO load/store access fault traps are not delegated to
> VS mode (hedeleg), M mode redirects them back to S mode.
> However, upon returning from M mode,the KVM executed in HS mode terminates
> VS mode software.
> KVM should redirect traps back to VS mode and let the VS mode trap handler
> determine the next steps.
> This is one approach to handling access fault traps in KVM,
> not only redirecting them to VS mode or terminating it.
>
> Signed-off-by: Yu-Wei Hsu <betterman5240@gmail.com>

Overall this patch looks good to me but the patch subject and
description can further simplified as follows:

    RISC-V: KVM: Redirect AMO load/store access fault traps to guest

    The KVM RISC-V does not delegate AMO load/store access fault traps to
    VS-mode (hedeleg) so typically M-mode takes these traps and redirects
    them back to HS-mode. However, upon returning from M-mode, the KVM
    RISC-V running in HS-mode terminates VS-mode software.

    The KVM RISC-V should redirect AMO load/store access fault traps back
    to VS-mode and let the VS-mode trap handler determine the next steps.

I have taken care of the above at the time of queuing this patch.

Reviewed-by: Anup Patel <anup@brainfault.org>

Queued this patch for Linux-6.11

Thanks,
Anup

> ---
>  arch/riscv/kvm/vcpu_exit.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
> index 2415722c01b8..ef8c5e3ec8a0 100644
> --- a/arch/riscv/kvm/vcpu_exit.c
> +++ b/arch/riscv/kvm/vcpu_exit.c
> @@ -185,6 +185,8 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
>         case EXC_INST_ILLEGAL:
>         case EXC_LOAD_MISALIGNED:
>         case EXC_STORE_MISALIGNED:
> +       case EXC_LOAD_ACCESS:
> +       case EXC_STORE_ACCESS:
>                 if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV) {
>                         kvm_riscv_vcpu_trap_redirect(vcpu, trap);
>                         ret = 1;
> --
> 2.25.1
>

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