RE: [PATCH V4 2/3] HYPERV/IOMMU: Add Hyper-V stub IOMMU driver

[Tianyu Lan <Tianyu.Lan@microsoft.com>]

Hi Michael:
               Thanks for your review.

-----Original Message-----
From: Michael Kelley <mikelley@microsoft.com> 
Sent: Friday, February 22, 2019 1:28 AM
To: lantianyu1986@gmail.com
Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>; joro@8bytes.org; mchehab+samsung@kernel.org; davem@davemloft.net; gregkh@linuxfoundation.org; nicolas.ferre@microchip.com; arnd@arndb.de; linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org; KY Srinivasan <kys@microsoft.com>; vkuznets <vkuznets@redhat.com>; alex.williamson@redhat.com; sashal@kernel.org; dan.carpenter@oracle.com; linux-hyperv@vger.kernel.org
Subject: RE: [PATCH V4 2/3] HYPERV/IOMMU: Add Hyper-V stub IOMMU driver

From: lantianyu1986@gmail.com <lantianyu1986@gmail.com> Sent: Monday, February 11, 2019 6:20 AM
> +	/*
> +	 * Hyper-V doesn't provide irq remapping function for
> +	 * IO-APIC and so IO-APIC only accepts 8-bit APIC ID.
> +	 * Cpu's APIC ID is read from ACPI MADT table and APIC IDs
> +	 * in the MADT table on Hyper-v are sorted monotonic increasingly.
> +	 * APIC ID reflects cpu topology. There maybe some APIC ID
> +	 * gaps when cpu number in a socket is not power of two. Prepare
> +	 * max cpu affinity for IOAPIC irqs. Scan cpu 0-255 and set cpu
> +	 * into ioapic_max_cpumask if its APIC ID is less than 256.
> +	 */
> +	for (i = min_t(unsigned int, num_possible_cpus(), 255); i >= 0; i--)

The above isn't quite right.  For example, if num_possible_cpus() is 8, then the loop will be executed 9 times, for values 8 down through 0.
It should be executed for values 7 down through 0.

Yes, fix this in the V5. Thanks.

> +		if (cpu_physical_id(i) < 256)
> +			cpumask_set_cpu(i, &ioapic_max_cpumask);
> +
> +	return 0;
> +}

Michael