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[81.97.203.96]) by smtp.gmail.com with ESMTPSA id m16-20020adffe50000000b00241bd7a7165sm38279954wrs.82.2023.01.04.07.18.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Jan 2023 07:18:29 -0800 (PST) Date: Wed, 4 Jan 2023 15:18:27 +0000 From: "Dr. David Alan Gilbert" To: Baoquan He , pbonzini@redhat.com, mlevitsk@redhat.com Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Thomas Gleixner , x86@kernel.org, kexec@lists.infradead.org Subject: Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support" Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Baoquan He (bhe@redhat.com) wrote: > On 12/20/22 at 12:38pm, Peter Zijlstra wrote: > > On Tue, Dec 20, 2022 at 01:34:58PM +0800, Baoquan He wrote: > > > This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92. > > > > > > On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal > > > kernel's cmdline, and triggering crash to jump to kdump kernel, kdump > > > kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic: > > > Implement IPI shorthands support") can fix it. > > > > > > The problem will disappear if removing 'nr_cpus=2' from normal kerne's > > > cmdline. > > > > And the root cause for this is... ? Does the kvm x2apic emulation > > somehow get upset when we shorthand CPUs that haven't been initialized? > > Thanks for checking. > > I haven't figure out the root cause. I haven't read the apic code for > long time, and not familiar with the kvm code. So raise the issue to > upstream. > > I can do testing if any suggestion. > > Add our virt dev Dr. David Alan Gilbert to CC. Hmm I don't know that code well enough; cc'ing Paolo and Maxim. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK