From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="KCxd4wLd" Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.9]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 922A2A7 for ; Thu, 14 Dec 2023 05:56:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1702562173; x=1734098173; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=6jOefrFXMRwcNHeUiKiN3C8daWx8ytPCTnAf310Jdx4=; b=KCxd4wLdruAdgy/fLaRIXXv9KSy58GkOXa4j0MSWaiWKbkpamLvo1vfb QT9waxVS/wfP+yL+8ydXMDPELbKEQh7Px9mxQX1OhOcF3j7i9PVCgBU1o qpDUDifJQHaH00XCXFAQHGKVgcTQCZZOxF1ktCW96PmyX8uOg48RTSY6C 3LydJ5HK2hUwImiGp693R8L0znseqzX7FcXJCUudZLHUye9DBvS+GJrR7 c9+BUYTk9/kLhmH7EiLc5ydw6mY1Wl9RxGeJxytQ5R3HggsiDwzH9blfo bDgHJ/j22QMx7kzY4KqC3Le1MKjxw49dm58gUanDVTHpOpj4YE1bK7Luz g==; X-IronPort-AV: E=McAfee;i="6600,9927,10924"; a="1972634" X-IronPort-AV: E=Sophos;i="6.04,275,1695711600"; d="scan'208";a="1972634" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Dec 2023 05:56:13 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10924"; a="840289972" X-IronPort-AV: E=Sophos;i="6.04,275,1695711600"; d="scan'208";a="840289972" Received: from liuzhao-optiplex-7080.sh.intel.com (HELO localhost) ([10.239.160.36]) by fmsmga008.fm.intel.com with ESMTP; 14 Dec 2023 05:56:10 -0800 Date: Thu, 14 Dec 2023 22:08:34 +0800 From: Zhao Liu To: Babu Moger Cc: pbonzini@redhat.com, richard.henderson@linaro.org, eduardo@habkost.net, mst@redhat.com, marcel.apfelbaum@gmail.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, Michael.Roth@amd.com, nikunj.dadhania@amd.com Subject: Re: [PATCH] target/i386: Fix CPUID encoding of Fn8000001E_ECX Message-ID: References: <20231110170806.70962-1-babu.moger@amd.com> 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-Disposition: inline In-Reply-To: <20231110170806.70962-1-babu.moger@amd.com> On Fri, Nov 10, 2023 at 11:08:06AM -0600, Babu Moger wrote: > Date: Fri, 10 Nov 2023 11:08:06 -0600 > From: Babu Moger > Subject: [PATCH] target/i386: Fix CPUID encoding of Fn8000001E_ECX > X-Mailer: git-send-email 2.34.1 > > Observed the following failure while booting the SEV-SNP guest and the > guest fails to boot with the smp parameters: > "-smp 192,sockets=1,dies=12,cores=8,threads=2". > > qemu-system-x86_64: sev_snp_launch_update: SNP_LAUNCH_UPDATE ret=-5 fw_error=22 'Invalid parameter' > qemu-system-x86_64: SEV-SNP: CPUID validation failed for function 0x8000001e, index: 0x0. > provided: eax:0x00000000, ebx: 0x00000100, ecx: 0x00000b00, edx: 0x00000000 > expected: eax:0x00000000, ebx: 0x00000100, ecx: 0x00000300, edx: 0x00000000 > qemu-system-x86_64: SEV-SNP: failed update CPUID page > > Reason for the failure is due to overflowing of bits used for "Node per > processor" in CPUID Fn8000001E_ECX. This field's width is 3 bits wide and > can hold maximum value 0x7. With dies=12 (0xB), it overflows and spills > over into the reserved bits. In the case of SEV-SNP, this causes CPUID > enforcement failure and guest fails to boot. > > The PPR documentation for CPUID_Fn8000001E_ECX [Node Identifiers] > ================================================================= > Bits Description > 31:11 Reserved. > > 10:8 NodesPerProcessor: Node per processor. Read-only. > ValidValues: > Value Description > 0h 1 node per processor. > 7h-1h Reserved. > > 7:0 NodeId: Node ID. Read-only. Reset: Fixed,XXh. > ================================================================= > > As in the spec, the valid value for "node per processor" is 0 and rest > are reserved. > > Looking back at the history of decoding of CPUID_Fn8000001E_ECX, noticed > that there were cases where "node per processor" can be more than 1. It > is valid only for pre-F17h (pre-EPYC) architectures. For EPYC or later > CPUs, the linux kernel does not use this information to build the L3 > topology. > > Also noted that the CPUID Function 0x8000001E_ECX is available only when > TOPOEXT feature is enabled. One additional query, such dependency relationship is not reflected in encode_topo_cpuid8000001e(), should TOPOEXT be checked in encode_topo_cpuid8000001e()? > This feature is enabled only for EPYC(F17h) > or later processors. So, previous generation of processors do not not > enumerate 0x8000001E_ECX leaf. > > There could be some corner cases where the older guests could enable the > TOPOEXT feature by running with -cpu host, in which case legacy guests > might notice the topology change. To address those cases introduced a > new CPU property "legacy-multi-node". It will be true for older machine > types to maintain compatibility. By default, it will be false, so new > decoding will be used going forward. > > The documentation is taken from Preliminary Processor Programming > Reference (PPR) for AMD Family 19h Model 11h, Revision B1 Processors 55901 > Rev 0.25 - Oct 6, 2022. > > Cc: qemu-stable@nongnu.org > Fixes: 31ada106d891 ("Simplify CPUID_8000_001E for AMD") > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 > Signed-off-by: Babu Moger > --- [snip] > +++ b/target/i386/cpu.h > @@ -1988,6 +1988,7 @@ struct ArchCPU { > * If true present the old cache topology information > */ > bool legacy_cache; > + bool legacy_multi_node; This property deserves a comment, as does legacy_cache above. > > /* Compatibility bits for old machine types: */ > bool enable_cpuid_0xb; > -- > 2.34.1 > Just the above nit, otherwise, Reviewed-by: Zhao Liu