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From: Ira Weiny <ira.weiny@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	nvdimm@lists.linux.dev, linux-mm@kvack.org
Subject: Re: [PATCH V7 03/18] x86/pks: Add additional PKEY helper macros
Date: Tue, 7 Dec 2021 16:51:06 -0800	[thread overview]
Message-ID: <20211208005106.GJ3538886@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <87lf1cl3cq.ffs@tglx>

On Thu, Nov 25, 2021 at 03:25:09PM +0100, Thomas Gleixner wrote:
> On Tue, Aug 03 2021 at 21:32, ira weiny wrote:
> > @@ -200,16 +200,14 @@ __setup("init_pkru=", setup_init_pkru);
> >   */
> >  u32 update_pkey_val(u32 pk_reg, int pkey, unsigned int flags)
> >  {
> > -	int pkey_shift = pkey * PKR_BITS_PER_PKEY;
> > -
> >  	/*  Mask out old bit values */
> > -	pk_reg &= ~(((1 << PKR_BITS_PER_PKEY) - 1) << pkey_shift);
> > +	pk_reg &= ~PKR_PKEY_MASK(pkey);
> >  
> >  	/*  Or in new values */
> >  	if (flags & PKEY_DISABLE_ACCESS)
> > -		pk_reg |= PKR_AD_BIT << pkey_shift;
> > +		pk_reg |= PKR_AD_KEY(pkey);
> >  	if (flags & PKEY_DISABLE_WRITE)
> > -		pk_reg |= PKR_WD_BIT << pkey_shift;
> > +		pk_reg |= PKR_WD_KEY(pkey);
> 
> I'm not seeing how this is improving that code. Quite the contrary.

Fair enough.  Even more so when using the code you suggested for pkey_update_pkval().

In that case it boils down to:

diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index eb6d6b872652..b7127329d115 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -198,7 +198,7 @@ __setup("init_pkru=", setup_init_pkru);
  */
 u32 pkey_update_pkval(u32 pkval, int pkey, u32 accessbits)
 {
-        int shift = pkey * PKR_BITS_PER_PKEY;
+        int shift = PKR_PKEY_SHIFT(pkey);
 
         if (WARN_ON_ONCE(accessbits & ~PKEY_ACCESS_MASK))
                 accessbits &= PKEY_ACCESS_MASK;


Better?

As to the reason of why to put this patch after the other one.  Why would I
improve the old pre-refactoring code only to throw it away when moving it to
pkey_update_pkval()?  This reasoning is even stronger when pkey_update_pkval()
is implemented.

I agree with Dan regarding the macros though.  I think they make it easier to
see what is going on without dealing with masks and shifts directly.  But I can
remove this patch if you feel that strongly about it.

Ira

> 
> Thanks,
> 
>         tglx

  parent reply	other threads:[~2021-12-08  0:51 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-04  4:32 [PATCH V7 00/18] PKS/PMEM: Add Stray Write Protection ira.weiny
2021-08-04  4:32 ` [PATCH V7 01/18] x86/pkeys: Create pkeys_common.h ira.weiny
2021-08-04  4:32 ` [PATCH V7 02/18] x86/fpu: Refactor arch_set_user_pkey_access() ira.weiny
2021-11-25 14:23   ` Thomas Gleixner
2021-08-04  4:32 ` [PATCH V7 03/18] x86/pks: Add additional PKEY helper macros ira.weiny
2021-11-25 14:25   ` Thomas Gleixner
2021-11-25 16:58     ` Thomas Gleixner
2021-12-08  0:51     ` Ira Weiny [this message]
2021-12-08 15:11       ` Thomas Gleixner
2021-08-04  4:32 ` [PATCH V7 04/18] x86/pks: Add PKS defines and Kconfig options ira.weiny
2021-08-04  4:32 ` [PATCH V7 05/18] x86/pks: Add PKS setup code ira.weiny
2021-11-25 15:15   ` Thomas Gleixner
2021-11-26  3:11     ` taoyi.ty
2021-11-26  9:57       ` Thomas Gleixner
2021-11-26 11:03     ` Thomas Gleixner
2021-08-04  4:32 ` [PATCH V7 06/18] x86/fault: Adjust WARN_ON for PKey fault ira.weiny
2021-08-04  4:32 ` [PATCH V7 07/18] x86/pks: Preserve the PKRS MSR on context switch ira.weiny
2021-11-25 15:25   ` Thomas Gleixner
2021-08-04  4:32 ` [PATCH V7 08/18] x86/entry: Preserve PKRS MSR across exceptions ira.weiny
2021-11-13  0:50   ` Ira Weiny
2021-11-25 11:19     ` Thomas Gleixner
2021-12-03  1:13     ` Andy Lutomirski
2021-11-25 14:12   ` Thomas Gleixner
2021-12-07  1:54     ` Ira Weiny
2021-12-07  4:45       ` Ira Weiny
2021-12-08  0:21       ` Thomas Gleixner
2021-08-04  4:32 ` [PATCH V7 09/18] x86/pks: Add PKS kernel API ira.weiny
2021-08-04  4:32 ` [PATCH V7 10/18] x86/pks: Introduce pks_abandon_protections() ira.weiny
2021-08-04  4:32 ` [PATCH V7 11/18] x86/pks: Add PKS Test code ira.weiny
2021-08-04  4:32 ` [PATCH V7 12/18] x86/pks: Add PKS fault callbacks ira.weiny
2021-08-11 21:18   ` Edgecombe, Rick P
2021-08-17  3:21     ` Ira Weiny
2021-08-04  4:32 ` [PATCH V7 13/18] memremap_pages: Add access protection via supervisor Protection Keys (PKS) ira.weiny
2021-08-04  4:32 ` [PATCH V7 14/18] memremap_pages: Add memremap.pks_fault_mode ira.weiny
2021-08-04  4:57   ` Randy Dunlap
2021-08-07 19:32     ` Ira Weiny
2021-08-11 19:01   ` Edgecombe, Rick P
2021-08-17  3:12     ` Ira Weiny
2021-08-04  4:32 ` [PATCH V7 15/18] kmap: Add stray access protection for devmap pages ira.weiny
2021-08-04  4:32 ` [PATCH V7 16/18] dax: Stray access protection for dax_direct_access() ira.weiny
2021-08-04  4:32 ` [PATCH V7 17/18] nvdimm/pmem: Enable stray access protection ira.weiny
2021-08-04  4:32 ` [PATCH V7 18/18] devdax: " ira.weiny

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