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

[Tianyu Lan]

Hi Michael:
               Thanks for your review.

-----Original Message-----
From: Michael Kelley <mikelley@xxxxxxxxxxxxx> 
Sent: Friday, February 22, 2019 1:28 AM
To: lantianyu1986@xxxxxxxxx
Cc: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>; joro@xxxxxxxxxx; mchehab+samsung@xxxxxxxxxx; davem@xxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; nicolas.ferre@xxxxxxxxxxxxx; arnd@xxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>; vkuznets <vkuznets@xxxxxxxxxx>; alex.williamson@xxxxxxxxxx; sashal@xxxxxxxxxx; dan.carpenter@xxxxxxxxxx; linux-hyperv@xxxxxxxxxxxxxxx
Subject: RE: [PATCH V4 2/3] HYPERV/IOMMU: Add Hyper-V stub IOMMU driver

From: lantianyu1986@xxxxxxxxx <lantianyu1986@xxxxxxxxx> 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