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X-CSE-ConnectionGUID: IntwzMNkSQaqZxTTsyE7IQ== X-CSE-MsgGUID: EQIT8tjvQLaeEF31+Z2hlg== X-IronPort-AV: E=McAfee;i="6800,10657,11569"; a="72726042" X-IronPort-AV: E=Sophos;i="6.18,307,1751266800"; d="scan'208";a="72726042" Received: from orviesa007.jf.intel.com ([10.64.159.147]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2025 11:00:18 -0700 X-CSE-ConnectionGUID: x+fPFCFnT9e7ut47tZ7pdw== X-CSE-MsgGUID: FXgySF4MQJeU0txcuCGGEA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.18,307,1751266800"; d="scan'208";a="178657151" Received: from gabaabhi-mobl2.amr.corp.intel.com (HELO [10.125.109.221]) ([10.125.109.221]) by orviesa007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2025 11:00:17 -0700 Message-ID: <2cbf11a4-fe92-483c-8ab7-182284720700@intel.com> Date: Wed, 1 Oct 2025 11:00:16 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/7] x86/kexec: Disable kexec/kdump on platforms with TDX partial write erratum To: Vishal Annapurve Cc: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, bp@alien8.de, tglx@linutronix.de, peterz@infradead.org, mingo@redhat.com, hpa@zytor.com, thomas.lendacky@amd.com, x86@kernel.org, kas@kernel.org, rick.p.edgecombe@intel.com, dwmw@amazon.co.uk, kai.huang@intel.com, seanjc@google.com, reinette.chatre@intel.com, isaku.yamahata@intel.com, dan.j.williams@intel.com, ashish.kalra@amd.com, nik.borisov@suse.com, chao.gao@intel.com, sagis@google.com, farrah.chen@intel.com, Binbin Wu References: <20250901160930.1785244-1-pbonzini@redhat.com> <20250901160930.1785244-5-pbonzini@redhat.com> <74a390a1-42a7-4e6b-a76a-f88f49323c93@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/1/25 10:17, Vishal Annapurve wrote: > And also mentions: > "Also note only the normal kexec needs to worry about this problem, but > not the crash kexec: 1) The kdump kernel only uses the special memory > reserved by the first kernel, and the reserved memory can never be used > by TDX in the first kernel; 2) The /proc/vmcore, which reflects the > first (crashed) kernel's memory, is only for read. The read will never > "poison" TDX memory thus cause unexpected machine check (only partial > write does)." > > What was the scenario that led to disabling kdump support altogether > given the above description? I think it was purely out of convenience so that the disabling could be three lines of code. I don't know off the top of my head if there's a simple enough way to disable kexec but not kdump. When I applied the thing, I was probably just considering kexec/kdump a monolithic thing and not thinking that folks would want one but not the other. Kai, did you have any other motivations?