linux-kernel - RE: [PATCH v5 09/10] x86/hyper-v: support extended CPU ranges for TLB flush hypercalls

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Date:   Tue, 30 May 2017 19:13:23 +0000
From:   Jork Loeser <Jork.Loeser@...rosoft.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "KY Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Simon Xiao <sixiao@...rosoft.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: RE: [PATCH v5 09/10] x86/hyper-v: support extended CPU ranges for TLB
 flush hypercalls

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Tuesday, May 30, 2017 04:34
> To: x86@...nel.org; devel@...uxdriverproject.org
> Cc: linux-kernel@...r.kernel.org; KY Srinivasan <kys@...rosoft.com>; Haiyang
> Zhang <haiyangz@...rosoft.com>; Stephen Hemminger
> <sthemmin@...rosoft.com>; Thomas Gleixner <tglx@...utronix.de>; Ingo
> Molnar <mingo@...hat.com>; H. Peter Anvin <hpa@...or.com>; Steven
> Rostedt <rostedt@...dmis.org>; Jork Loeser <Jork.Loeser@...rosoft.com>;
> Simon Xiao <sixiao@...rosoft.com>; Andy Lutomirski <luto@...nel.org>; Andy
> Shevchenko <andy.shevchenko@...il.com>
> Subject: [PATCH v5 09/10] x86/hyper-v: support extended CPU ranges for TLB
> flush hypercalls
> 
> Hyper-V hosts may support more than 64 vCPUs, we need to use
> HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX/LIST_EX hypercalls in this case.


> +static inline int cpumask_to_vp_set(struct hv_flush_pcpu_ex *flush,
> +				    const struct cpumask *cpus)
> +{
> +	int cpu, vcpu, vcpu_bank, vcpu_offset, cur_bank, nr_bank = 0;
> +	bool has_cpus;
> +
> +	/*
> +	 * We can't be sure that translated vCPU numbers will always be
> +	 * in ascending order, so iterate over all possible banks and
> +	 * check all vCPUs in it instead.
> +	 */
> +	for (cur_bank = 0; cur_bank < ms_hyperv.max_vp_index/64;
> cur_bank++) {
> +		has_cpus = false;
> +		for_each_cpu(cpu, cpus) {
> +			vcpu = hv_cpu_number_to_vp_number(cpu);
> +			vcpu_bank = vcpu / 64;
> +			vcpu_offset = vcpu % 64;
> +
> +			if (vcpu_bank != cur_bank)
> +				continue;
> +			__set_bit(vcpu_offset, (unsigned long *)
> +				  &flush->hv_vp_set.bank_contents[nr_bank]);
> +			if (!has_cpus) {
> +				__set_bit(vcpu_bank, (unsigned long *)
> +					  &flush->hv_vp_set.valid_bank_mask);
> +				has_cpus = true;
> +			}
> +		}
> +		if (has_cpus)
> +			nr_bank++;
> +	}
> +
> +	return nr_bank;
> +}

Note that the HV_VP_SET may contain empty banks. As such, consider enabling all (5) bits in the valid_bank_mask, and a single for_each(cpu, cpus) pass - setting the bits as per hv_cpu_number_to_vp_number(cpu).

Regards,
Jork