From: Ira Weiny <ira.weiny@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Andy Lutomirski <luto@kernel.org>,
Fenghua Yu <fenghua.yu@intel.com>,
x86@kernel.org, Dave Hansen <dave.hansen@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
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 04/17] x86/pks: Preserve the PKRS MSR on context switch
Date: Fri, 17 Jul 2020 14:39:30 -0700 [thread overview]
Message-ID: <20200717213929.GR3008823@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200717083140.GW10769@hirez.programming.kicks-ass.net>
On Fri, Jul 17, 2020 at 10:31:40AM +0200, Peter Zijlstra wrote:
> On Fri, Jul 17, 2020 at 12:20:43AM -0700, ira.weiny@intel.com wrote:
>
> > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> > index f362ce0d5ac0..d69250a7c1bf 100644
> > --- a/arch/x86/kernel/process.c
> > +++ b/arch/x86/kernel/process.c
> > @@ -42,6 +42,7 @@
> > #include <asm/spec-ctrl.h>
> > #include <asm/io_bitmap.h>
> > #include <asm/proto.h>
> > +#include <asm/pkeys_internal.h>
> >
> > #include "process.h"
> >
> > @@ -184,6 +185,36 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
> > return ret;
> > }
> >
> > +/*
> > + * NOTE: We wrap pks_init_task() and pks_sched_in() with
> > + * CONFIG_ARCH_HAS_SUPERVISOR_PKEYS because using IS_ENABLED() fails
> > + * due to the lack of task_struct->saved_pkrs in this configuration.
> > + * Furthermore, we place them here because of the complexity introduced by
> > + * header conflicts introduced to get the task_struct definition in the pkeys
> > + * headers.
> > + */
>
> I don't see anything much useful in that comment.
I'm happy to delete. Internal reviews questioned the motive here so I added
the comment to inform why this style was chosen rather than the preferred
IS_ENABLED().
I've deleted it now.
>
> > +#ifdef CONFIG_ARCH_HAS_SUPERVISOR_PKEYS
> > +DECLARE_PER_CPU(u32, pkrs_cache);
> > +static inline void pks_init_task(struct task_struct *tsk)
> > +{
> > + /* New tasks get the most restrictive PKRS value */
> > + tsk->thread.saved_pkrs = INIT_PKRS_VALUE;
> > +}
> > +static inline void pks_sched_in(void)
> > +{
> > + u64 current_pkrs = current->thread.saved_pkrs;
> > +
> > + /* Only update the MSR when current's pkrs is different from the MSR. */
> > + if (this_cpu_read(pkrs_cache) == current_pkrs)
> > + return;
> > +
> > + write_pkrs(current_pkrs);
>
> Should we write that like:
>
> /*
> * PKRS is only temporarily changed during specific code paths.
> * Only a preemption during these windows away from the default
> * value would require updating the MSR.
> */
> if (unlikely(this_cpu_read(pkrs_cache) != current_pkrs))
> write_pkrs(current_pkrs);
>
> ?
Yes I think the unlikely is better.
Thanks,
Ira
>
> > +}
> > +#else
> > +static inline void pks_init_task(struct task_struct *tsk) { }
> > +static inline void pks_sched_in(void) { }
> > +#endif
next prev parent reply other threads:[~2020-07-17 21:39 UTC|newest]
Thread overview: 73+ 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 ` [PATCH RFC V2 01/17] x86/pkeys: Create pkeys_internal.h 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 8:54 ` Peter Zijlstra
2020-07-17 20:52 ` Ira Weiny
2020-07-20 9:14 ` Peter Zijlstra
2020-07-17 22:36 ` Dave Hansen
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 ` [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch ira.weiny
2020-07-17 8:31 ` Peter Zijlstra
2020-07-17 21:39 ` Ira Weiny [this message]
2020-07-17 8:59 ` Peter Zijlstra
2020-07-17 22:34 ` Ira Weiny
2020-07-20 9:15 ` Peter Zijlstra
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 ` [PATCH RFC V2 06/17] x86/pks: Add a debugfs file for allocated PKS keys 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 ` [PATCH RFC V2 08/17] x86/pks: Add PKS Test code 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 ` [PATCH RFC V2 10/17] fs/dax: Remove unused size parameter 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 ` [PATCH RFC V2 12/17] memremap: Add zone device access protection ira.weiny
2020-07-17 9:10 ` Peter Zijlstra
2020-07-18 5:06 ` Ira Weiny
2020-07-20 9:16 ` Peter Zijlstra
2020-07-17 9:17 ` Peter Zijlstra
2020-07-18 5:51 ` Ira Weiny
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 9:21 ` Peter Zijlstra
2020-07-19 4:13 ` Ira Weiny
2020-07-20 9:17 ` Peter Zijlstra
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 9:22 ` Peter Zijlstra
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 ` [PATCH RFC V2 16/17] [dax|pmem]: Enable stray write protection ira.weiny
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 9:30 ` Peter Zijlstra
2020-07-21 18:01 ` Ira Weiny
2020-07-21 19:11 ` Peter Zijlstra
2020-07-17 9:34 ` Peter Zijlstra
2020-07-17 10:06 ` Peter Zijlstra
2020-07-22 5:27 ` Ira Weiny
2020-07-22 9:48 ` Peter Zijlstra
2020-07-22 21:24 ` Ira Weiny
2020-07-23 20:08 ` Thomas Gleixner
2020-07-23 20:15 ` Thomas Gleixner
2020-07-24 17:23 ` Ira Weiny
2020-07-24 17:29 ` Andy Lutomirski
2020-07-24 19:43 ` Ira Weiny
2020-07-22 16:21 ` Andy Lutomirski
2020-07-23 16:18 ` Fenghua Yu
2020-07-23 16:23 ` Dave Hansen
2020-07-23 16:52 ` Fenghua Yu
2020-07-23 17:08 ` Andy Lutomirski
2020-07-23 17:30 ` Dave Hansen
2020-07-23 20:23 ` Thomas Gleixner
2020-07-23 20:22 ` Thomas Gleixner
2020-07-23 21:30 ` Andy Lutomirski
2020-07-23 22:14 ` Thomas Gleixner
2020-07-23 19:53 ` Thomas Gleixner
2020-07-23 22:04 ` Ira Weiny
2020-07-23 23:41 ` Thomas Gleixner
2020-07-24 21:24 ` Thomas Gleixner
2020-07-24 21:31 ` Thomas Gleixner
2020-07-25 0:09 ` Andy Lutomirski
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
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