Re: [PATCH v2 01/13] KVM: s390: pv: avoid stall notifications for some UVCs

Janosch Frank
2021-07-29T09:58:48Z

On 7/28/21 4:26 PM, Claudio Imbrenda wrote:
> Improve make_secure_pte to avoid stalls when the system is heavily
> overcommitted. This was especially problematic in kvm_s390_pv_unpack,
> because of the loop over all pages that needed unpacking.
>
> Also fix kvm_s390_pv_init_vm to avoid stalls when the system is heavily
> overcommitted.

Fixes tag?

>
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
> arch/s390/kernel/uv.c | 11 ++++++++---
> arch/s390/kvm/pv.c | 2 +-
> 2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index aeb0a15bcbb7..fd0faa51c1bb 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -196,11 +196,16 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
> if (!page_ref_freeze(page, expected))
> return -EBUSY;
> set_bit(PG_arch_1, &page->flags);
> - rc = uv_call(0, (u64)uvcb);
> + rc = __uv_call(0, (u64)uvcb);

We should exchange rc with cc since that's what we get back from
__uv_call(). Technically we always get a cc but for the other functions
it's only ever 0/1 which translates to success/error so rc is ok.

> page_ref_unfreeze(page, expected);
> - /* Return -ENXIO if the page was not mapped, -EINVAL otherwise */
> - if (rc)
> + /*
> + * Return -ENXIO if the page was not mapped, -EINVAL for other errors.
> + * If busy or partially completed, return -EAGAIN.
> + */
> + if (rc == 1)
> rc = uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
> + else if (rc > 1)
> + rc = -EAGAIN;
> return rc;

Could you define the CCs in uv.h and check against the constants here so
it's easier to understand that the rc > 1 checks against a "UV was busy
please re-issue the call again" cc?

Maybe also make it explicit for cc 2 and 3 instead of cc > 1

> }
>
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index c8841f476e91..e007df11a2fe 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -196,7 +196,7 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
> uvcb.conf_base_stor_origin = (u64)kvm->arch.pv.stor_base;
> uvcb.conf_virt_stor_origin = (u64)kvm->arch.pv.stor_var;
>
> - cc = uv_call(0, (u64)&uvcb);
> + cc = uv_call_sched(0, (u64)&uvcb);
> *rc = uvcb.header.rc;
> *rrc = uvcb.header.rrc;
> KVM_UV_EVENT(kvm, 3, "PROTVIRT CREATE VM: handle %llx len %llx rc %x rrc %x",
>