linux-kernel - RE: [PATCH] x86/hyperv: Enable 15-bit APIC ID if the hypervisor supports it

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Message-ID: <MWHPR21MB154620E39FDDF862E8906249BF110@MWHPR21MB1546.namprd21.prod.outlook.com>
Date:   Tue, 3 Nov 2020 09:37:06 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        vkuznets <vkuznets@...hat.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>
Subject: RE: [PATCH] x86/hyperv: Enable 15-bit APIC ID if the hypervisor
 supports it

> From: Dexuan Cui <decui@...rosoft.com>
> Sent: Monday, November 2, 2020 5:12 PM
> 
> ...

Hi tglx,
Now this patch is in the x86/apic branch, which is great! Thanks for the 
quick action! But the third line of the below paragraph of the commit log
is missing... Sorry I just realized I should have not prefixed that line with the
">255 APIC IDs" -- it looks a line is ignored if it starts with 2 chars of ">>". :-(

> On an old Hyper-V host that doesn't support the Extended Dest ID, nothing
> changes with this commit: Linux VM is still able to bring up the CPUs with
> >255 APIC IDs with the help of hyperv-iommu.c, but IOAPIC interrupts still
> can not go to such CPUs, and the kdump kernel still can not work properly
> on such CPUs.