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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 02/17] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support
Date: Fri, 17 Jul 2020 13:52:55 -0700
Message-ID: <20200717205254.GQ3008823@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200717085442.GX10769@hirez.programming.kicks-ass.net>

On Fri, Jul 17, 2020 at 10:54:42AM +0200, Peter Zijlstra wrote:
> On Fri, Jul 17, 2020 at 12:20:41AM -0700, ira.weiny@intel.com wrote:
> > +/*
> > + * Get a new pkey register value from the user values specified.
> > + *
> > + * Kernel users use the same flags as user space:
> > + *     PKEY_DISABLE_ACCESS
> > + *     PKEY_DISABLE_WRITE
> > + */
> > +u32 get_new_pkr(u32 old_pkr, int pkey, unsigned long init_val)
> > +{
> > +	int pkey_shift = (pkey * PKR_BITS_PER_PKEY);
> > +	u32 new_pkr_bits = 0;
> > +
> > +	/* Set the bits we need in the register:  */
> > +	if (init_val & PKEY_DISABLE_ACCESS)
> > +		new_pkr_bits |= PKR_AD_BIT;
> > +	if (init_val & PKEY_DISABLE_WRITE)
> > +		new_pkr_bits |= PKR_WD_BIT;
> > +
> > +	/* Shift the bits in to the correct place: */
> > +	new_pkr_bits <<= pkey_shift;
> > +
> > +	/* Mask off any old bits in place: */
> > +	old_pkr &= ~((PKR_AD_BIT | PKR_WD_BIT) << pkey_shift);
> > +
> > +	/* Return the old part along with the new part: */
> > +	return old_pkr | new_pkr_bits;
> > +}
> 
> This is unbelievable junk...
> 
> How about something like:
> 
> u32 update_pkey_reg(u32 pk_reg, int pkey, unsigned int flags)
> {
> 	int pkey_shift = pkey * PKR_BITS_PER_PKEY;
> 
> 	pk_reg &= ~(((1 << PKR_BITS_PER_PKEY) - 1) << pkey_shift);
> 
> 	if (flags & PKEY_DISABLE_ACCESS)
> 		pk_reg |= PKR_AD_BIT << pkey_shift;
> 	if (flags & PKEY_DISABLE_WRITE)
> 		pk_reg |= PKR_WD_BIT << pkey_shift;
> 
> 	return pk_reg;
> }
> 
> Then we at least have a little clue wtf the thing does.. Yes I started
> with a rename and then got annoyed at the implementation too.

On the code I think this is fair.  I've also updated the calling function to be
a bit cleaner as well.

However, I think the name 'update' is a bit misleading.  Here is the new
calling code:

...
        pkru = read_pkru();
	pkru = update_pkey_reg(pkru, pkey, init_val);
	write_pkru(pkru);
...


I think it is odd to have a function called update_pkey_reg() called right
before a write_pkru().  Can we call this update_pkey_value?  or just 'val'?
Because write_pkru() actually updates the register.

Thanks for the review,
Ira


  reply index

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 [this message]
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
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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