[PATCH] RISC-V: KVM: Exit run-loop immediately if xfer_to_guest fails

[PATCH] RISC-V: KVM: Exit run-loop immediately if xfer_to_guest fails

[Anup Patel]

If xfer_to_guest_mode_handle_work() fails in the run-loop then exit
the run-loop immediately instead of doing it after some more work.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
---
 arch/riscv/kvm/vcpu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 71ebbc4821f0..17d5b3f8c2ee 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -984,8 +984,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 	while (ret > 0) {
 		/* Check conditions before entering the guest */
 		ret = xfer_to_guest_mode_handle_work(vcpu);
-		if (!ret)
-			ret = 1;
+		if (ret)
+			continue;
+		ret = 1;
 
 		kvm_riscv_gstage_vmid_update(vcpu);
 
-- 
2.34.1

Re: [PATCH] RISC-V: KVM: Exit run-loop immediately if xfer_to_guest fails

[Andreas Schwab]

On Nov 08 2022, Anup Patel wrote:

> If xfer_to_guest_mode_handle_work() fails in the run-loop then exit
> the run-loop immediately instead of doing it after some more work.
>
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> ---
>  arch/riscv/kvm/vcpu.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 71ebbc4821f0..17d5b3f8c2ee 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -984,8 +984,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  	while (ret > 0) {
>  		/* Check conditions before entering the guest */
>  		ret = xfer_to_guest_mode_handle_work(vcpu);
> -		if (!ret)
> -			ret = 1;
> +		if (ret)
> +			continue;

If that is supposed to exit the loop, it would be clearer to just use
break.

> +		ret = 1;

There is a condition on ret <= 0 later in the loop that no longer can be
true.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

Re: [PATCH] RISC-V: KVM: Exit run-loop immediately if xfer_to_guest fails

[Anup Patel]

On Tue, Nov 8, 2022 at 5:48 PM Andreas Schwab <schwab@suse.de> wrote:
>
> On Nov 08 2022, Anup Patel wrote:
>
> > If xfer_to_guest_mode_handle_work() fails in the run-loop then exit
> > the run-loop immediately instead of doing it after some more work.
> >
> > Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> > Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> > ---
> >  arch/riscv/kvm/vcpu.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> > index 71ebbc4821f0..17d5b3f8c2ee 100644
> > --- a/arch/riscv/kvm/vcpu.c
> > +++ b/arch/riscv/kvm/vcpu.c
> > @@ -984,8 +984,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
> >       while (ret > 0) {
> >               /* Check conditions before entering the guest */
> >               ret = xfer_to_guest_mode_handle_work(vcpu);
> > -             if (!ret)
> > -                     ret = 1;
> > +             if (ret)
> > +                     continue;
>
> If that is supposed to exit the loop, it would be clearer to just use
> break.

This is a convention within the run-loop that we continue whenever
whenever "ret" is no longer suitable to continue. I don't see any
particular advantage in breaking this convention over here.

>
> > +             ret = 1;
>
> There is a condition on ret <= 0 later in the loop that no longer can be
> true.

Yes, for now the "ret <= 0" check is useless and the compiler will
optimize this comparison. We will be soon having more stuff added
to run-loop (such as AIA update) which will make "ret <= 0" check
useful again.

>
> --
> Andreas Schwab, SUSE Labs, schwab@suse.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."

Queued this patch for Linux-6.2

Thanks,
Anup