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X-CSE-ConnectionGUID: Qz9Mf9BbR2K/FVAJyj1vkQ== X-CSE-MsgGUID: bjhVmKBQQPmMvkmO6DUGXQ== X-IronPort-AV: E=McAfee;i="6800,10657,11745"; a="75272309" X-IronPort-AV: E=Sophos;i="6.23,153,1770624000"; d="scan'208";a="75272309" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by fmvoesa112.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Apr 2026 08:02:56 -0700 X-CSE-ConnectionGUID: z+My3eUxS0uH0ZEAm0HmDA== X-CSE-MsgGUID: w0yt8C68SCmiiGs1Ht19og== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,153,1770624000"; d="scan'208";a="221855782" Received: from dnelso2-mobl.amr.corp.intel.com (HELO [10.125.111.95]) ([10.125.111.95]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Apr 2026 08:02:55 -0700 Message-ID: <830f1e46-0fb7-4756-827b-c8f46af24374@intel.com> Date: Wed, 1 Apr 2026 08:03:02 -0700 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/5] x86/virt/tdx: Pull kexec cache flush logic into arch/x86 To: Sean Christopherson , Rick P Edgecombe Cc: Vishal L Verma , Kai Huang , "bp@alien8.de" , "x86@kernel.org" , "kas@kernel.org" , "hpa@zytor.com" , "mingo@redhat.com" , "linux-kernel@vger.kernel.org" , "dave.hansen@linux.intel.com" , "tglx@kernel.org" , "pbonzini@redhat.com" , "linux-coco@lists.linux.dev" , "kvm@vger.kernel.org" References: <20260323-fuller_tdx_kexec_support-v2-0-87a36409e051@intel.com> <20260323-fuller_tdx_kexec_support-v2-2-87a36409e051@intel.com> <6ad3ff51bbab85147b716de0b1f4e8b994b1998b.camel@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 3/31/26 16:04, Sean Christopherson wrote: > But unless the WBINVD is actually costly, why bother getting fancy? WBINVD might be the most expensive single instruction in the whole ISA. That said, I'd much rather have a potentially unnecessary WBINVD than miss one. The thing I'd be worried about would be something wonky like: 1. CPU offline does WBINVD 2. Some other TDX call gets made, dirties caches again 3. tdx_offline_cpu() skips WBINVD So, let's just do both for now: Do WBINVD in tdx_offline_cpu() and comment that it might be redundant with other things in the CPU offline procedure. This really needs to be solved with infrastructure and keeping data about the reasons for needing WBINVD, not relying on code ordering or fragile semantics.