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From: Thomas Gleixner <tglx@linutronix.de>
To: Dexuan Cui <decui@microsoft.com>,
	dwmw@amazon.co.uk, x86@kernel.org, decui@microsoft.com,
	mikelley@microsoft.com, linux-hyperv@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, Tianyu.Lan@microsoft.com,
	vkuznets@redhat.com, kys@microsoft.com, haiyangz@microsoft.com,
	sthemmin@microsoft.com, wei.liu@kernel.org
Subject: Re: [PATCH] iommu/hyper-v: Fix panic on a host without the 15-bit APIC ID support
Date: Wed, 02 Dec 2020 10:56:23 +0100	[thread overview]
Message-ID: <87wny0edko.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201202004510.1818-1-decui@microsoft.com>

On Tue, Dec 01 2020 at 16:45, Dexuan Cui wrote:
> The commit f36a74b9345a itself is good, but it causes a panic in a
> Linux VM that runs on a Hyper-V host that doesn't have the 15-bit
> Extended APIC ID support:
>     kernel BUG at arch/x86/kernel/apic/io_apic.c:2408!

This has nothing to do with the 15bit APIC ID support, really.

The point is that the select() function only matches when I/O APIC ID is
0, which is not guaranteed. That's independent of the 15bit extended
APIC ID feature. But the I/O-APIC ID is irrelevant on hyperv because
there is only one.

> This happens because the Hyper-V ioapic_ir_domain (which is defined in
> drivers/iommu/hyperv-iommu.c) can not be found. Fix the panic by
> properly claiming the only I/O APIC emulated by Hyper-V.

We don't fix a panic. We fix a bug in the code :)

I'll amend the changelog.

Thanks,

        tglx

  parent reply	other threads:[~2020-12-02  9:57 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-02  0:45 [PATCH] iommu/hyper-v: Fix panic on a host without the 15-bit APIC ID support Dexuan Cui
2020-12-02  1:28 ` Woodhouse, David
2020-12-02  9:56 ` Thomas Gleixner [this message]
2020-12-02 19:53   ` Dexuan Cui
2020-12-02 10:28 ` [tip: x86/apic] iommu/hyper-v: Remove I/O-APIC ID check from hyperv_irq_remapping_select() tip-bot2 for Dexuan Cui

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