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From: Peter Zijlstra <peterz@infradead.org>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Andy Lutomirski <luto@amacapital.net>,
	Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
	Dave Martin <Dave.Martin@arm.com>
Subject: Re: [PATCH v8 11/27] x86/mm: Introduce _PAGE_DIRTY_SW
Date: Wed, 28 Aug 2019 09:03:08 +0200
Message-ID: <20190828070308.GJ2332@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <6c3dc33e16c8bbb6d45c0a6ec7c684de197fa065.camel@intel.com>

On Tue, Aug 27, 2019 at 03:37:12PM -0700, Yu-cheng Yu wrote:
> On Fri, 2019-08-23 at 16:02 +0200, Peter Zijlstra wrote:
> > On Tue, Aug 13, 2019 at 01:52:09PM -0700, Yu-cheng Yu wrote:
> > 
> > > +static inline pte_t pte_move_flags(pte_t pte, pteval_t from, pteval_t to)
> > > +{
> > > +	if (pte_flags(pte) & from)
> > > +		pte = pte_set_flags(pte_clear_flags(pte, from), to);
> > > +	return pte;
> > > +}
> > 
> > Aside of the whole conditional thing (I agree it would be better to have
> > this unconditionally); the function doesn't really do as advertised.
> > 
> > That is, if @from is clear, it doesn't endeavour to make sure @to is
> > also clear.
> > 
> > Now it might be sufficient, but in that case it really needs a comment
> > and or different name.
> > 
> > An implementation that actually moves the bit is something like:
> > 
> > 	pteval_t a,b;
> > 
> > 	a = native_pte_value(pte);
> > 	b = (a >> from_bit) & 1;
> > 	a &= ~((1ULL << from_bit) | (1ULL << to_bit));
> > 	a |= b << to_bit;
> > 	return make_native_pte(a);
> 
> There can be places calling pte_wrprotect() on a PTE that is already RO +
> DIRTY_SW.  Then in pte_move_flags(pte, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW) we do not
>  want to clear _PAGE_DIRTY_SW.  But, I will look into this and make it more
> obvious.

Well, then the name 'move' is just wrong, because that is not the
semantics you're looking for.

So the thing is; if you provide a generic function that 'munges' two
bits, then it's name had better be accurate. But AFAICT you only ever
used this for the DIRTY bits, so it might be better to have a function
specifically for that and with a comment that spells out the exact
semantics and reasons for them.


  reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 20:51 [PATCH v8 00/27] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2019-08-13 20:51 ` [PATCH v8 01/27] Documentation/x86: Add CET description Yu-cheng Yu
2019-08-14  8:07   ` Florian Weimer
2019-08-14 15:57     ` Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 02/27] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2019-08-21 10:20   ` Borislav Petkov
2019-08-21 14:46     ` Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 03/27] x86/fpu/xstate: Change names to separate XSAVES system and user states Yu-cheng Yu
2019-08-21 14:45   ` Borislav Petkov
2019-08-13 20:52 ` [PATCH v8 04/27] x86/fpu/xstate: Introduce XSAVES system states Yu-cheng Yu
2019-08-16 19:56   ` Thomas Gleixner
2019-08-16 19:59     ` Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 05/27] x86/fpu/xstate: Introduce CET MSR " Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 06/27] x86/cet: Add control protection exception handler Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 07/27] x86/cet/shstk: Add Kconfig option for user-mode shadow stack Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 08/27] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 09/27] mm/mmap: Prevent Shadow Stack VMA merges Yu-cheng Yu
2019-08-13 22:34   ` Dave Hansen
2019-08-14 16:20     ` Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 10/27] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 11/27] x86/mm: Introduce _PAGE_DIRTY_SW Yu-cheng Yu
2019-08-13 23:02   ` Dave Hansen
2019-08-13 23:49     ` Andy Lutomirski
2019-08-14 16:42     ` Yu-cheng Yu
2019-08-14 16:58       ` Dave Hansen
2019-08-23 14:02   ` Peter Zijlstra
2019-08-27 22:37     ` Yu-cheng Yu
2019-08-28  7:03       ` Peter Zijlstra [this message]
2019-08-28 14:57         ` Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 12/27] drm/i915/gvt: Update _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 13/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 14/27] x86/mm: Shadow stack page fault error checking Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 15/27] mm: Handle shadow stack page fault Yu-cheng Yu
2019-08-13 22:55   ` Andy Lutomirski
2019-08-14 16:27     ` Yu-cheng Yu
2019-08-14 16:48       ` Dave Hansen
2019-08-14 17:00         ` Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 16/27] mm: Handle THP/HugeTLB " Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 17/27] mm: Update can_follow_write_pte/pmd for shadow stack Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 18/27] mm: Introduce do_mmap_locked() Yu-cheng Yu
2019-08-20  1:02   ` Sean Christopherson
2019-08-20 16:08     ` Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 19/27] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 20/27] x86/cet/shstk: Introduce WRUSS instruction Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 21/27] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file Yu-cheng Yu
2019-08-16 13:55   ` Dave Martin
2019-08-20 10:02   ` Dave Martin
2019-08-13 20:52 ` [PATCH v8 23/27] x86/cet/shstk: ELF header parsing of Shadow Stack Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 24/27] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 25/27] mm/mmap: Add Shadow stack pages to memory accounting Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 26/27] x86/cet/shstk: Add arch_prctl functions for Shadow Stack Yu-cheng Yu
2019-08-13 20:52 ` [PATCH v8 27/27] x86/cet/shstk: Add Shadow Stack instructions to opcode map Yu-cheng Yu

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