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

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Message-ID: <aAsonR1r7esKxjNR@liuwe-devbox-ubuntu-v2.tail21d00.ts.net>
Date: Fri, 25 Apr 2025 06:15:57 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: bp@...en8.de, dave.hansen@...ux.intel.com, decui@...rosoft.com,
	haiyangz@...rosoft.com, hpa@...or.com, kys@...rosoft.com,
	mikelley@...rosoft.com, mingo@...hat.com, tglx@...utronix.de,
	tiala@...rosoft.com, wei.liu@...nel.org,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, apais@...rosoft.com, benhill@...rosoft.com,
	bperkins@...rosoft.com, sunilmut@...rosoft.com
Subject: Re: [PATCH hyperv-next] x86/hyperv: Fix APIC ID and VP ID confusion
 in hv_snp_boot_ap()

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.