2022-11-08 12:26:58

by Anup Patel

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

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

2022-11-08 12:31:30

by Andreas Schwab

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

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 <[email protected]>
> Reviewed-by: Andrew Jones <[email protected]>
> ---
> 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, [email protected]
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

2022-11-27 12:53:31

by Anup Patel

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

On Tue, Nov 8, 2022 at 5:48 PM Andreas Schwab <[email protected]> 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 <[email protected]>
> > Reviewed-by: Andrew Jones <[email protected]>
> > ---
> > 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, [email protected]
> 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