Hi Thomas and Vitaly
Sorry for the late reply. I was buried in my other work.
On Tue, Oct 05, 2021 at 02:53:29PM +0200, Vitaly Kuznetsov wrote:
> Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes:
>
> > Wei!
> >
>
> Not Wei here but I don't see the question answered on the mailing list
> so let me give my thoughts.
>
> > On Fri, Sep 10 2021 at 18:57, Wei Liu wrote:
> >> -static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector)
> >> +static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector,
> >> + bool exclude_self)
> >> {
> >> struct hv_send_ipi_ex **arg;
> >> struct hv_send_ipi_ex *ipi_arg;
> >> @@ -123,7 +124,10 @@ static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector)
> >>
> >> if (!cpumask_equal(mask, cpu_present_mask)) {
> >
> > Not part of that patch, but is checking cpu_present_mask correct here?
> > If so then this really lacks a comment for the casual reader.
>
> It seems it *was* correct prior to 'exclude_self': the idea is that for
> everything but 'cpu_present_mask' we use HV_GENERIC_SET_SPARSE_4K
> format, for 'cpu_present_mask' we just use 'all' (HV_GENERIC_SET_ALL)
> to avoid specifying individual CPUs.
Yes, that's the intent.
It was correct before because cpumask would have been filtered to
exclude "self" when it came to this function.
>
> >
> >> ipi_arg->vp_set.format = HV_GENERIC_SET_SPARSE_4K;
> >> - nr_bank = cpumask_to_vpset(&(ipi_arg->vp_set), mask);
> >> + if (exclude_self)
> >> + nr_bank = cpumask_to_vpset_noself(&(ipi_arg->vp_set), mask);
> >> + else
> >> + nr_bank = cpumask_to_vpset(&(ipi_arg->vp_set), mask);
> >> }
> >
> > But, what happens in the case that mask == cpu_present_mask and
> > exclude_self == true?
> >
> > AFAICT it ends up sending the IPI to all CPUs including self:
> >
> > if (!nr_bank)
> > ipi_arg->vp_set.format = HV_GENERIC_SET_ALL;
> >
> > Not entirely correct, right?
>
> It's not, I think we need something like (completely untested)
>
> diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
> index 32a1ad356c18..80b7660208e4 100644
> --- a/arch/x86/hyperv/hv_apic.c
> +++ b/arch/x86/hyperv/hv_apic.c
> @@ -122,17 +122,17 @@ static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector,
> ipi_arg->reserved = 0;
> ipi_arg->vp_set.valid_bank_mask = 0;
>
> - if (!cpumask_equal(mask, cpu_present_mask)) {
> + if (!cpumask_equal(mask, cpu_present_mask) || exclude_self) {
> ipi_arg->vp_set.format = HV_GENERIC_SET_SPARSE_4K;
> if (exclude_self)
> nr_bank = cpumask_to_vpset_noself(&(ipi_arg->vp_set), mask);
> else
> nr_bank = cpumask_to_vpset(&(ipi_arg->vp_set), mask);
> - }
> - if (nr_bank < 0)
> - goto ipi_mask_ex_done;
> - if (!nr_bank)
> + if (nr_bank =< 0)
> + goto ipi_mask_ex_done;
> + } else {
> ipi_arg->vp_set.format = HV_GENERIC_SET_ALL;
> + }
>
> status = hv_do_rep_hypercall(HVCALL_SEND_IPI_EX, 0, nr_bank,
> ipi_arg, NULL);
>
> here. Wei, I can test and send this out if you're not on it already.
>
Please turn this into a patch and send it out. Thank you so much for
looking into it.
Wei.
> --
> Vitaly
>
