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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Wei Liu <wei.liu@kernel.org>,
        Linux on Hyper-V List <linux-hyperv@vger.kernel.org>
Cc:     Michael Kelley <mikelley@microsoft.com>, kys@microsoft.com,
        haiyangz@microsoft.com, decui@microsoft.com,
        sthemmin@microsoft.com, Wei Liu <wei.liu@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] x86/hyperv: remove on-stack cpumask from
 hv_send_ipi_mask_allbutself
In-Reply-To: <20210910185714.299411-3-wei.liu@kernel.org>
References: <20210910185714.299411-1-wei.liu@kernel.org>
 <20210910185714.299411-3-wei.liu@kernel.org>
Date:   Mon, 27 Sep 2021 00:03:10 +0200
Message-ID: <87ee9batb5.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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