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Fri, 19 Dec 2025 00:47:27 -0800 (PST) Received: from imammedo ([213.175.37.14]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324ea1aef7sm3718542f8f.7.2025.12.19.00.47.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Dec 2025 00:47:27 -0800 (PST) Date: Fri, 19 Dec 2025 09:47:26 +0100 From: Igor Mammedov To: Sean Christopherson Cc: Paolo Bonzini , kvm@vger.kernel.org, Peter Xu Subject: Re: [kvm-unit-tests PATCH] x86/cstart: Delete "local" version of save_id() to fix x2APIC SMP bug Message-ID: <20251219094726.5f970468@imammedo> In-Reply-To: <20251218232618.2504147-1-seanjc@google.com> References: <20251218232618.2504147-1-seanjc@google.com> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 18 Dec 2025 15:26:18 -0800 Sean Christopherson wrote: > Delete cstart.S's version of save_id() to play nice with 32-bit SMP tests > on CPUs that support x2APIC. The local version assumes xAPIC mode and so > depending on the underlying "hardware" (e.g. AVIC vs. APICv vs. emulated, > and with or without KVM_X86_QUIRK_LAPIC_MMIO_HOLE), may mark the wrong CPU > as being online. > > Fixes: 0991c0ea ("x86: fix APs with APIC ID more that 255 not showing in id_map") > Cc: Igor Mammedov > Cc: Peter Xu > Signed-off-by: Sean Christopherson Acked-by: Igor Mammedov > --- > x86/cstart.S | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/x86/cstart.S b/x86/cstart.S > index dafb330d..49ba4818 100644 > --- a/x86/cstart.S > +++ b/x86/cstart.S > @@ -84,13 +84,6 @@ prepare_32: > > smp_stacktop: .long stacktop - per_cpu_size > > -save_id: > - movl $(APIC_DEFAULT_PHYS_BASE + APIC_ID), %eax > - movl (%eax), %eax > - shrl $24, %eax > - lock btsl %eax, online_cpus > - retl > - > ap_start32: > setup_segments > mov $-per_cpu_size, %esp > > base-commit: 31d91f5c9b7546471b729491664b05c933d64a7a