linux-kernel - Re: [PATCH v2 2/2] x86/hyperv: remove on-stack cpumask from hv_send_ipi_mask

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Date:   Mon, 27 Sep 2021 00:03:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>
Cc:     Michael Kelley <mikelley@...rosoft.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, decui@...rosoft.com,
        sthemmin@...rosoft.com, Wei Liu <wei.liu@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] x86/hyperv: remove on-stack cpumask from
 hv_send_ipi_mask_allbutself

Wei!

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.

>  		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?

Thanks,

        tglx