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From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
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 07:57:41 -0700	[thread overview]
Message-ID: <29e6afa9cd7a7b0069ec6b999a2830cbbbe50a56.camel@intel.com> (raw)
In-Reply-To: <20190828070308.GJ2332@hirez.programming.kicks-ass.net>

On Wed, 2019-08-28 at 09:03 +0200, Peter Zijlstra wrote:
> 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.

Yes, I will work on that.

Yu-cheng


  reply	other threads:[~2019-08-28 15:07 UTC|newest]

Thread overview: 55+ 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
2019-08-28 14:57         ` Yu-cheng Yu [this message]
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
2019-11-08 13:27   ` Adrian Hunter
2019-11-08 18:09     ` Yu-cheng Yu

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