linux-kernel - RE: [EXTERNAL] Re: [PATCH hyperv-next] x86/hyperv: Fix APIC ID and VP ID confusion in hv_snp_boot

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Message-ID:
 <KUZP153MB14448BEFA81251661433CE33BE842@KUZP153MB1444.APCP153.PROD.OUTLOOK.COM>
Date: Fri, 25 Apr 2025 17:18:40 +0000
From: Saurabh Singh Sengar <ssengar@...rosoft.com>
To: Roman Kisel <romank@...ux.microsoft.com>, Wei Liu <wei.liu@...nel.org>
CC: "bp@...en8.de" <bp@...en8.de>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, Dexuan Cui <decui@...rosoft.com>, Haiyang
 Zhang <haiyangz@...rosoft.com>, "hpa@...or.com" <hpa@...or.com>, KY
 Srinivasan <kys@...rosoft.com>, "mikelley@...rosoft.com"
	<mikelley@...rosoft.com>, "mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, Tianyu Lan
	<Tianyu.Lan@...rosoft.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, Allen Pais
	<apais@...rosoft.com>, Ben Hillis <Ben.Hillis@...rosoft.com>, Brian Perkins
	<Brian.Perkins@...rosoft.com>, Sunil Muthuswamy <sunilmut@...rosoft.com>
Subject: RE: [EXTERNAL] Re: [PATCH hyperv-next] x86/hyperv: Fix APIC ID and VP
 ID confusion in hv_snp_boot_ap()

 
> On 4/25/2025 2:14 AM, Saurabh Singh Sengar wrote:
> >>
> >> On Thu, Apr 24, 2025 at 02:57:46PM -0700, Roman Kisel wrote:
> >>> To start an application processor in SNP-isolated guest, a hypercall
> >>> is used that takes a virtual processor index. The hv_snp_boot_ap()
> >>> function uses that START_VP hypercall but passes as VP ID to it what
> >>> it receives as a wakeup_secondary_cpu_64 callback: the APIC ID.
> >>>
> >>> As those two aren't generally interchangeable, that may lead to hung
> >>> APs if VP IDs and APIC IDs don't match, e.g. APIC IDs might be
> >>> sparse whereas VP IDs never are.
> >>>
> >>> Update the parameter names to avoid confusion as to what the
> >>> parameter is. Use the APIC ID to VP ID conversion to provide correct
> >>> input to the hypercall.
> >>>
> >>> Cc: stable@...r.kernel.org
> >>> Fixes: 44676bb9d566 ("x86/hyperv: Add smp support for SEV-SNP
> >>> guest")
> >>> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
> >>
> >> Applied to hyperv-fixes.
> >
> > This patch will break the builds.
> >
> > Roman,
> > Have you tested this patch on the latest linux-next ?
> 
> Thanks for your help! Only on hyperv-next, looking how to repro and fix on
> linux-next. The kernel robot was happy, or I am missing some context about
> how the robot works...
> 
> What was your kernel configuration, or just anything that enables Hyper-V?
> 
> I thought the the linux-next tree would be a subset of hyper-next so should
> work, realizing that have to check, likely there might be changes from other
> trees.
> 


hyperv-fixes is broken too, here's the log for your ref:

https://dashboard.kernelci.org/log-viewer?itemId=microsoft%3A20250425085833916790&o=microsoft&type=build&url=https%3A%2F%2Flisalogsb15850d3.blob.core.windows.net%2Flisa-logs%2Fdefault_default%2F20250425%2F20250425-085110-393%2Fkernel_installer%2Fbuild.log%3Fst%3D2025-04-25T09%253A09%253A35Z%26se%3D2025-05-02T09%253A09%253A35Z%26sp%3Dr%26sv%3D2024-11-04%26sr%3Db%26skoid%3D14b53b1d-f4fc-442e-a437-4989376b1754%26sktid%3D72f988bf-86f1-41af-91ab-2d7cd011db47%26skt%3D2025-04-25T09%253A09%253A35Z%26ske%3D2025-05-02T09%253A09%253A35Z%26sks%3Db%26skv%3D2024-11-04%26sig%3DZHfA7%2FC174KR6HT8zhchCb47NE1aceqw8h0APzKxsII%253D

The hv_snp_boot_ap() function in arch/x86/hyperv/ivm.c currently fails to compile.
It looks like the function's argument was changed from 'cpu' to 'apic_id', but internal
references to cpu were not updated accordingly.

This might have gone unnoticed during your testing if CONFIG_AMD_MEM_ENCRYPT
was disabled, in which case this function wouldn't have been compiled.

Regards,
Saurabh