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: <aAv6slMtA7Kioy_3@liuwe-devbox-ubuntu-v2.tail21d00.ts.net>
Date: Fri, 25 Apr 2025 21:12:18 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: Saurabh Singh Sengar <ssengar@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, "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 Fri, Apr 25, 2025 at 11:22:08AM -0700, Roman Kisel wrote:
> 
> 
> On 4/25/2025 10:18 AM, Saurabh Singh Sengar wrote:
> > > 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.
> 
> Must be the case! I did run the command to merge the CVM specific config
> options but I didn't check the result.
> 
> Yep, I see the issue. Will resend the patch.

I have removed this from hyperv-fixes.