From: Thomas Gleixner <tglx@linutronix.de> To: Ira Weiny <ira.weiny@intel.com> Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, Andrew Morton <akpm@linux-foundation.org>, Fenghua Yu <fenghua.yu@intel.com>, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions Date: Fri, 24 Jul 2020 01:41:20 +0200 [thread overview] Message-ID: <87mu3pvly7.fsf@nanos.tec.linutronix.de> (raw) In-Reply-To: <20200723220435.GI844235@iweiny-DESK2.sc.intel.com> Ira, Ira Weiny <ira.weiny@intel.com> writes: > On Thu, Jul 23, 2020 at 09:53:20PM +0200, Thomas Gleixner wrote: > I think, after fixing my code (see below), using idtentry_state could still > work. If the per-cpu cache and the MSR is updated in idtentry_exit() that > should carry the state to the new cpu, correct? I'm way too tired to think about that now. Will have a look tomorrow with brain awake. >> > It seems like we should start passing this by reference instead of >> > value. But for now this works as an RFC. Comments? >> >> Works as in compiles, right? >> >> static void noinstr idt_save_pkrs(idtentry_state_t state) >> { >> state.foo = 1; >> } >> >> How is that supposed to change the caller state? C programming basics. > > <sigh> I am so stupid. I was not looking at this particular case but you are > 100% correct... I can't believe I did not see this. > > In the above statement I was only thinking about the extra overhead I was > adding to idtentry_enter() and the callers of it. Fun. That statement immediately caught my attention and made me look at that function. > "C programming basics" indeed... Once again sorry... Don't worry. One interesting design bug of the human brain is that it tricks you into seeing what you expect to see no matter how hard you try not to fall for that. You can spend days staring at the obvious without seeing it. The saying 'you can't see the forest for the trees' exists for a reason. Yes, I know it's embarrassing, but that happens and it happens to all of us no matter how experienced we are. Just search the LKML archives for 'brown paperbag'. You'll find amazing things. If you show your problem to people who are not involved in that at all there is a high propability that it immediately snaps for one of them. But there is no guarantee, just look at this mail thread and the number of people who did not notice. Move on and accept the fact that it will happen again :) Thanks, tglx _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org
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From: Thomas Gleixner <tglx@linutronix.de> To: Ira Weiny <ira.weiny@intel.com> Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, Dan Williams <dan.j.williams@intel.com>, Vishal Verma <vishal.l.verma@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Fenghua Yu <fenghua.yu@intel.com>, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions Date: Fri, 24 Jul 2020 01:41:20 +0200 [thread overview] Message-ID: <87mu3pvly7.fsf@nanos.tec.linutronix.de> (raw) In-Reply-To: <20200723220435.GI844235@iweiny-DESK2.sc.intel.com> Ira, Ira Weiny <ira.weiny@intel.com> writes: > On Thu, Jul 23, 2020 at 09:53:20PM +0200, Thomas Gleixner wrote: > I think, after fixing my code (see below), using idtentry_state could still > work. If the per-cpu cache and the MSR is updated in idtentry_exit() that > should carry the state to the new cpu, correct? I'm way too tired to think about that now. Will have a look tomorrow with brain awake. >> > It seems like we should start passing this by reference instead of >> > value. But for now this works as an RFC. Comments? >> >> Works as in compiles, right? >> >> static void noinstr idt_save_pkrs(idtentry_state_t state) >> { >> state.foo = 1; >> } >> >> How is that supposed to change the caller state? C programming basics. > > <sigh> I am so stupid. I was not looking at this particular case but you are > 100% correct... I can't believe I did not see this. > > In the above statement I was only thinking about the extra overhead I was > adding to idtentry_enter() and the callers of it. Fun. That statement immediately caught my attention and made me look at that function. > "C programming basics" indeed... Once again sorry... Don't worry. One interesting design bug of the human brain is that it tricks you into seeing what you expect to see no matter how hard you try not to fall for that. You can spend days staring at the obvious without seeing it. The saying 'you can't see the forest for the trees' exists for a reason. Yes, I know it's embarrassing, but that happens and it happens to all of us no matter how experienced we are. Just search the LKML archives for 'brown paperbag'. You'll find amazing things. If you show your problem to people who are not involved in that at all there is a high propability that it immediately snaps for one of them. But there is no guarantee, just look at this mail thread and the number of people who did not notice. Move on and accept the fact that it will happen again :) Thanks, tglx
next prev parent reply other threads:[~2020-07-23 23:41 UTC|newest] Thread overview: 157+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-17 7:20 [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 01/17] x86/pkeys: Create pkeys_internal.h ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 02/17] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 8:54 ` Peter Zijlstra 2020-07-17 8:54 ` Peter Zijlstra 2020-07-17 20:52 ` Ira Weiny 2020-07-17 20:52 ` Ira Weiny 2020-07-20 9:14 ` Peter Zijlstra 2020-07-20 9:14 ` Peter Zijlstra 2020-07-17 22:36 ` Dave Hansen 2020-07-17 22:36 ` Dave Hansen 2020-07-20 9:13 ` Peter Zijlstra 2020-07-20 9:13 ` Peter Zijlstra 2020-07-17 7:20 ` [PATCH RFC V2 03/17] x86/pks: Enable Protection Keys Supervisor (PKS) ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 8:31 ` Peter Zijlstra 2020-07-17 8:31 ` Peter Zijlstra 2020-07-17 21:39 ` Ira Weiny 2020-07-17 21:39 ` Ira Weiny 2020-07-17 8:59 ` Peter Zijlstra 2020-07-17 8:59 ` Peter Zijlstra 2020-07-17 22:34 ` Ira Weiny 2020-07-17 22:34 ` Ira Weiny 2020-07-20 9:15 ` Peter Zijlstra 2020-07-20 9:15 ` Peter Zijlstra 2020-07-20 18:35 ` Ira Weiny 2020-07-20 18:35 ` Ira Weiny 2020-07-17 7:20 ` [PATCH RFC V2 05/17] x86/pks: Add PKS kernel API ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 06/17] x86/pks: Add a debugfs file for allocated PKS keys ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 07/17] Documentation/pkeys: Update documentation for kernel pkeys ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 08/17] x86/pks: Add PKS Test code ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 09/17] memremap: Convert devmap static branch to {inc,dec} ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 10/17] fs/dax: Remove unused size parameter ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 11/17] drivers/dax: Expand lock scope to cover the use of addresses ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 12/17] memremap: Add zone device access protection ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:10 ` Peter Zijlstra 2020-07-17 9:10 ` Peter Zijlstra 2020-07-18 5:06 ` Ira Weiny 2020-07-18 5:06 ` Ira Weiny 2020-07-20 9:16 ` Peter Zijlstra 2020-07-20 9:16 ` Peter Zijlstra 2020-07-17 9:17 ` Peter Zijlstra 2020-07-17 9:17 ` Peter Zijlstra 2020-07-18 5:51 ` Ira Weiny 2020-07-18 5:51 ` Ira Weiny 2020-07-17 9:20 ` Peter Zijlstra 2020-07-17 9:20 ` Peter Zijlstra 2020-07-17 7:20 ` [PATCH RFC V2 13/17] kmap: Add stray write protection for device pages ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:21 ` Peter Zijlstra 2020-07-17 9:21 ` Peter Zijlstra 2020-07-19 4:13 ` Ira Weiny 2020-07-19 4:13 ` Ira Weiny 2020-07-20 9:17 ` Peter Zijlstra 2020-07-20 9:17 ` Peter Zijlstra 2020-07-21 16:31 ` Ira Weiny 2020-07-21 16:31 ` Ira Weiny 2020-07-17 7:20 ` [PATCH RFC V2 14/17] dax: Stray write protection for dax_direct_access() ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:22 ` Peter Zijlstra 2020-07-17 9:22 ` Peter Zijlstra 2020-07-19 4:41 ` Ira Weiny 2020-07-19 4:41 ` Ira Weiny 2020-07-17 7:20 ` [PATCH RFC V2 15/17] nvdimm/pmem: Stray write protection for pmem->virt_addr ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 16/17] [dax|pmem]: Enable stray write protection ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:25 ` Peter Zijlstra 2020-07-17 9:25 ` Peter Zijlstra 2020-07-17 7:20 ` [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:30 ` Peter Zijlstra 2020-07-17 9:30 ` Peter Zijlstra 2020-07-21 18:01 ` Ira Weiny 2020-07-21 18:01 ` Ira Weiny 2020-07-21 19:11 ` Peter Zijlstra 2020-07-21 19:11 ` Peter Zijlstra 2020-07-17 9:34 ` Peter Zijlstra 2020-07-17 9:34 ` Peter Zijlstra 2020-07-17 10:06 ` Peter Zijlstra 2020-07-17 10:06 ` Peter Zijlstra 2020-07-22 5:27 ` Ira Weiny 2020-07-22 5:27 ` Ira Weiny 2020-07-22 9:48 ` Peter Zijlstra 2020-07-22 9:48 ` Peter Zijlstra 2020-07-22 21:24 ` Ira Weiny 2020-07-22 21:24 ` Ira Weiny 2020-07-23 20:08 ` Thomas Gleixner 2020-07-23 20:08 ` Thomas Gleixner 2020-07-23 20:15 ` Thomas Gleixner 2020-07-23 20:15 ` Thomas Gleixner 2020-07-24 17:23 ` Ira Weiny 2020-07-24 17:23 ` Ira Weiny 2020-07-24 17:29 ` Andy Lutomirski 2020-07-24 17:29 ` Andy Lutomirski 2020-07-24 19:43 ` Ira Weiny 2020-07-24 19:43 ` Ira Weiny 2020-07-22 16:21 ` Andy Lutomirski 2020-07-22 16:21 ` Andy Lutomirski 2020-07-22 16:21 ` Andy Lutomirski 2020-07-23 16:18 ` Fenghua Yu 2020-07-23 16:18 ` Fenghua Yu 2020-07-23 16:18 ` Fenghua Yu 2020-07-23 16:23 ` Dave Hansen 2020-07-23 16:23 ` Dave Hansen 2020-07-23 16:23 ` Dave Hansen 2020-07-23 16:52 ` Fenghua Yu 2020-07-23 16:52 ` Fenghua Yu 2020-07-23 16:52 ` Fenghua Yu 2020-07-23 17:08 ` Andy Lutomirski 2020-07-23 17:08 ` Andy Lutomirski 2020-07-23 17:08 ` Andy Lutomirski 2020-07-23 17:30 ` Dave Hansen 2020-07-23 17:30 ` Dave Hansen 2020-07-23 17:30 ` Dave Hansen 2020-07-23 20:23 ` Thomas Gleixner 2020-07-23 20:23 ` Thomas Gleixner 2020-07-23 20:23 ` Thomas Gleixner 2020-07-23 20:22 ` Thomas Gleixner 2020-07-23 20:22 ` Thomas Gleixner 2020-07-23 20:22 ` Thomas Gleixner 2020-07-23 21:30 ` Andy Lutomirski 2020-07-23 21:30 ` Andy Lutomirski 2020-07-23 21:30 ` Andy Lutomirski 2020-07-23 22:14 ` Thomas Gleixner 2020-07-23 22:14 ` Thomas Gleixner 2020-07-23 22:14 ` Thomas Gleixner 2020-07-23 19:53 ` Thomas Gleixner 2020-07-23 19:53 ` Thomas Gleixner 2020-07-23 22:04 ` Ira Weiny 2020-07-23 22:04 ` Ira Weiny 2020-07-23 23:41 ` Thomas Gleixner [this message] 2020-07-23 23:41 ` Thomas Gleixner 2020-07-24 21:24 ` Thomas Gleixner 2020-07-24 21:24 ` Thomas Gleixner 2020-07-24 21:31 ` Thomas Gleixner 2020-07-24 21:31 ` Thomas Gleixner 2020-07-25 0:09 ` Andy Lutomirski 2020-07-25 0:09 ` Andy Lutomirski 2020-07-25 0:09 ` Andy Lutomirski 2020-07-27 20:59 ` Ira Weiny 2020-07-27 20:59 ` Ira Weiny 2020-07-24 22:19 ` [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support Kees Cook 2020-07-24 22:19 ` Kees Cook
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