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[192.55.54.38]) by smtp.gmail.com with ESMTPSA id u1-v6sm3838600pgk.25.2018.07.20.05.34.19 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 20 Jul 2018 05:34:19 -0700 (PDT) Received: by kshutemo-mobl1.localdomain (Postfix, from userid 1000) id 1C1E6300254; Fri, 20 Jul 2018 15:34:16 +0300 (+03) Date: Fri, 20 Jul 2018 15:34:16 +0300 From: "Kirill A. Shutemov" To: Thomas Gleixner Cc: Dave Hansen , "Kirill A. Shutemov" , Ingo Molnar , x86@kernel.org, "H. Peter Anvin" , Tom Lendacky , Kai Huang , Jacob Pan , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCHv5 08/19] x86/mm: Introduce variables to store number, shift and mask of KeyIDs Message-ID: <20180720123415.57m2fqbdjtvnietu@kshutemo-mobl1> References: <20180717112029.42378-1-kirill.shutemov@linux.intel.com> <20180717112029.42378-9-kirill.shutemov@linux.intel.com> <1edc05b0-8371-807e-7cfa-6e8f61ee9b70@intel.com> <20180719102130.b4f6b6v5wg3modtc@kshutemo-mobl1> <20180719131245.sxnqsgzvkqriy3o2@kshutemo-mobl1> <20180719132312.75lduymla2uretax@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180622 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 19, 2018 at 03:40:41PM +0200, Thomas Gleixner wrote: > On Thu, 19 Jul 2018, Kirill A. Shutemov wrote: > > On Thu, Jul 19, 2018 at 03:18:03PM +0200, Thomas Gleixner wrote: > > > On Thu, 19 Jul 2018, Kirill A. Shutemov wrote: > > > > On Thu, Jul 19, 2018 at 02:37:35PM +0200, Thomas Gleixner wrote: > > > > > On Thu, 19 Jul 2018, Kirill A. Shutemov wrote: > > > > > > On Wed, Jul 18, 2018 at 04:19:10PM -0700, Dave Hansen wrote: > > > > > > > > } else { > > > > > > > > /* > > > > > > > > * Reset __PHYSICAL_MASK. > > > > > > > > @@ -591,6 +592,9 @@ static void detect_tme(struct cpuinfo_x86 *c) > > > > > > > > * between CPUs. > > > > > > > > */ > > > > > > > > physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1; > > > > > > > > + mktme_keyid_mask = 0; > > > > > > > > + mktme_keyid_shift = 0; > > > > > > > > + mktme_nr_keyids = 0; > > > > > > > > } > > > > > > > > > > > > > > Should be unnecessary. These are zeroed by the compiler. > > > > > > > > > > > > No. detect_tme() called for each CPU in the system. > > > > > > > > > > And then the variables are cleared out while other CPUs can access them? > > > > > How is that supposed to work? > > > > > > > > This code path only matter in patalogical case: when MKTME configuation is > > > > inconsitent between CPUs. Basically if BIOS screwed things up we disable > > > > MKTME. > > > > > > I still don't see how that's supposed to work. > > > > > > When the inconsistent CPU is brought up _AFTER_ MKTME is enabled, then how > > > does clearing the variables help? It does not magically make all the other > > > stuff go away. > > > > We don't actually enable MKTME in kernel. BIOS does. Kernel makes choose > > to use it or not. Current design targeted to be used by userspace. > > So until init we don't have any other stuff to go away. We can just > > pretend that MKTME was never there. > > Hotplug is not guaranteed to happen _BEFORE_ init. Think about physical > hotplug. Ouch. I didn't think about this. :/ In this case I don't see how to handle the situation properly. Is it okay to WARN() && pray()? -- Kirill A. Shutemov