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X-CSE-ConnectionGUID: vZoovKDsRzq2roo3QDS2YA== X-CSE-MsgGUID: ZOigfAxtQMqvYTXTv9F/WA== X-IronPort-AV: E=McAfee;i="6700,10204,11315"; a="47832195" X-IronPort-AV: E=Sophos;i="6.12,314,1728975600"; d="scan'208";a="47832195" Received: from orviesa009.jf.intel.com ([10.64.159.149]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jan 2025 07:05:48 -0800 X-CSE-ConnectionGUID: upyu2WiaTzapl2Q/qkiJFg== X-CSE-MsgGUID: KHszczQHTy622aP0cp8j2w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,314,1728975600"; d="scan'208";a="104594911" Received: from ssimmeri-mobl2.amr.corp.intel.com (HELO [10.124.223.199]) ([10.124.223.199]) by orviesa009-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jan 2025 07:05:47 -0800 Message-ID: <6737e3d6-65fa-46b3-9413-e26f4ba8efdd@intel.com> Date: Tue, 14 Jan 2025 07:05:48 -0800 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 v4 05/12] x86/mm: add INVLPGB support code To: Tom Lendacky , Rik van Riel , x86@kernel.org Cc: linux-kernel@vger.kernel.org, bp@alien8.de, peterz@infradead.org, dave.hansen@linux.intel.com, zhengqi.arch@bytedance.com, nadav.amit@gmail.com, kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, jannh@google.com References: <20250112155453.1104139-1-riel@surriel.com> <20250112155453.1104139-6-riel@surriel.com> <685632f2-44a4-a7fd-063b-1d426896f297@amd.com> <7045d1666ac5722820a43fffa7f2e6fb3c2eb485.camel@surriel.com> <5085e0aa-5921-40c2-c018-c947b98f5152@amd.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 1/14/25 06:29, Tom Lendacky wrote: >> Given the choice between "a bug in the calling code >> crashes the kernel" and "a bug in the calling code >> results in a missed TLB flush", I'm guessing the >> crash is probably better. > So instead of the negative number protection, shouldn't this just use an > unsigned int for extra_count and panic() if the value is greater than > invlpgb_count_max? The caller has some sort of logic problem and it > could possibly result in missed TLB flushes. Or if a panic() is out of > the question, maybe a WARN() and a full TLB flush to be safe? The current implementation will panic in the #GP handler though. It should be pretty easy to figure out that INVLPGB is involved with RIP or the Code: snippet. From there, you'd need to figure out what caused the #GP. I guess the one nasty thing is that a person debugging this might not have a CPUID dump handy so wouldn't actually know the number of valid addresses that INVLPGB can take. But otherwise, I'm not sure an explicit panic adds _much_ value here over an implicit one via the #GP handler. I don't know how everybody else feels about it, but I'm happy just depending on the #GP for now.