From: Ira Weiny <ira.weiny@intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V8 41/44] kmap: Ensure kmap works for devmap pages
Date: Tue, 1 Mar 2022 15:03:09 -0800 [thread overview]
Message-ID: <Yh6mLd8ORTcLx18A@iweiny-desk3> (raw)
In-Reply-To: <CAPcyv4g+Cbqk5bev8=SNz-8EwzofER0HrTzUiJ87ygdWSsXAiA@mail.gmail.com>
On Tue, Mar 01, 2022 at 12:05:27PM -0800, Dan Williams wrote:
> On Tue, Mar 1, 2022 at 11:45 AM Ira Weiny <ira.weiny@intel.com> wrote:
> >
> > On Fri, Feb 04, 2022 at 01:07:10PM -0800, Dan Williams wrote:
> > > On Thu, Jan 27, 2022 at 9:55 AM <ira.weiny@intel.com> wrote:
> > > >
> > > > From: Ira Weiny <ira.weiny@intel.com>
> > > >
> > > > Users of devmap pages should not have to know that the pages they are
> > > > operating on are special.
> > >
> > > How about get straight to the point without any ambiguous references:
> > >
> > > Today, kmap_{local_page,atomic} handles granting access to HIGHMEM
> > > pages without the caller needing to know if the page is HIGHMEM, or
> > > not. Use that existing infrastructure to grant access to PKS/PGMAP
> > > access protected pages.
> >
> > This sounds better. Thanks.
> >
> > >
> > > > Co-opt the kmap_{local_page,atomic}() to mediate access to PKS protected
> > > > pages via the devmap facility. kmap_{local_page,atomic}() are both
> > > > thread local mappings so they work well with the thread specific
> > > > protections available.
> > > >
> > > > kmap(), on the other hand, allows for global mappings to be established,
> > > > Which is incompatible with the underlying PKS facility.
> > >
> > > Why is kmap incompatible with PKS? I know why, but this is a claim
> > > without evidence. If you documented that in a previous patch, there's
> > > no harm and copying and pasting into this one. A future git log user
> > > will thank you for not making them go to lore to try to find the one
> > > patch with the details.
> >
> > Good point.
> >
> > > Extra credit for creating a PKS theory of
> > > operation document with this detail, unless I missed that?
> >
> > Well... I've documented and mentioned the thread-local'ness of PKS a lot but
> > I'm pretty close to all of this so it is hard for me to remember where and to
> > what degree that is documented. I've already reworked the PKS documentation a
> > bit. So I'll review that.
> >
> > >
> > > > For this reason
> > > > kmap() is not supported. Rather than leave the kmap mappings to fault
> > > > at random times when users may access them,
> > >
> > > Is that a problem?
> >
> > No.
>
> What I meant was how random is random and is it distinguishable from
> direct page_address() usage where there is no explicit early failure
> path?
Ok you've convinced me. I'll drop this.
>
> >
> > > This instrumentation is also insufficient for
> > > legitimate usages of page_address().
> >
> > True. Although with this protection those access' are no longer legitimate.
> > And it sounds like it may be worth putting a call in page_address() as well.
> >
> > > Might as well rely on the kernel
> > > developer community being able to debug PKS WARN() splats back to the
> > > source because that will need to be done regardless, given kmap() is
> > > not the only source of false positive access violations.
> >
> > I disagree but I'm happy to drop pgmap_protection_flag_invalid() if that is the
> > consensus.
> >
> > The reason I disagree is that it is generally better to catch errors early
> > rather than later. Furthermore, this does not change the permissions. Which
> > means the actual invalid access will also get flagged at the point of use.
> > This allows more debugging information for the user.
> >
> > Do you feel that strongly about removing pgmap_protection_flag_invalid()?
>
> You haven't convinced me that it matters yet. Do you have an example
> of a kmap() pointer dereference PKS splat where it's not clear from
> the backtrace from the fault handler that a kmap path was involved?
>
> At a minimum if it stays it seems like something that should be
> wrapped by VM_WARN_ON_ONCE_PAGE() like other page relative memory
> debugging extra checks that get disabled by CONFIG_DEBUG_VM, but the
> assertion that "early is better" needs evidence that "later is too
> ambiguous".
I'll drop this. It is easier to just leave it out.
Ira
next prev parent reply other threads:[~2022-03-01 23:03 UTC|newest]
Thread overview: 145+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-27 17:54 [PATCH V8 00/44] PKS/PMEM: Add Stray Write Protection ira.weiny
2022-01-27 17:54 ` [PATCH V8 01/44] entry: Create an internal irqentry_exit_cond_resched() call ira.weiny
2022-01-27 17:54 ` [PATCH V8 02/44] Documentation/protection-keys: Clean up documentation for User Space pkeys ira.weiny
2022-01-28 22:39 ` Dave Hansen
2022-02-01 23:49 ` Ira Weiny
2022-02-01 23:54 ` Dave Hansen
2022-01-27 17:54 ` [PATCH V8 03/44] x86/pkeys: Create pkeys_common.h ira.weiny
2022-01-28 22:43 ` Dave Hansen
2022-02-02 1:00 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 04/44] x86/pkeys: Add additional PKEY helper macros ira.weiny
2022-01-28 22:47 ` Dave Hansen
2022-02-02 20:21 ` Ira Weiny
2022-02-02 20:26 ` Dave Hansen
2022-02-02 20:28 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 05/44] x86/fpu: Refactor arch_set_user_pkey_access() ira.weiny
2022-01-28 22:50 ` Dave Hansen
2022-02-02 20:22 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 06/44] mm/pkeys: Add Kconfig options for PKS ira.weiny
2022-01-28 22:54 ` Dave Hansen
2022-01-28 23:10 ` Ira Weiny
2022-01-28 23:51 ` Dave Hansen
2022-02-04 19:08 ` Ira Weiny
2022-02-09 5:34 ` Ira Weiny
2022-02-14 19:20 ` Dave Hansen
2022-02-14 23:03 ` Ira Weiny
2022-01-29 0:06 ` Dave Hansen
2022-02-04 19:14 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 07/44] x86/pkeys: Add PKS CPU feature bit ira.weiny
2022-01-28 23:05 ` Dave Hansen
2022-02-04 19:21 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 08/44] x86/fault: Adjust WARN_ON for PKey fault ira.weiny
2022-01-28 23:10 ` Dave Hansen
2022-02-04 20:06 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 09/44] x86/pkeys: Enable PKS on cpus which support it ira.weiny
2022-01-28 23:18 ` Dave Hansen
2022-01-28 23:41 ` Ira Weiny
2022-01-28 23:53 ` Dave Hansen
2022-01-27 17:54 ` [PATCH V8 10/44] Documentation/pkeys: Add initial PKS documentation ira.weiny
2022-01-28 23:57 ` Dave Hansen
2022-01-27 17:54 ` [PATCH V8 11/44] mm/pkeys: Define static PKS key array and default values ira.weiny
2022-01-29 0:02 ` Dave Hansen
2022-02-04 23:54 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 12/44] mm/pkeys: Define PKS page table macros ira.weiny
2022-01-27 17:54 ` [PATCH V8 13/44] mm/pkeys: Add initial PKS Test code ira.weiny
2022-01-31 19:30 ` Edgecombe, Rick P
2022-02-09 23:44 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 14/44] x86/pkeys: Introduce pks_write_pkrs() ira.weiny
2022-01-29 0:12 ` Dave Hansen
2022-01-29 0:16 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 15/44] x86/pkeys: Preserve the PKS MSR on context switch ira.weiny
2022-01-29 0:22 ` Dave Hansen
2022-02-11 6:10 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 16/44] mm/pkeys: Introduce pks_mk_readwrite() ira.weiny
2022-01-31 23:10 ` Edgecombe, Rick P
2022-02-18 2:22 ` Ira Weiny
2022-02-01 17:40 ` Dave Hansen
2022-02-18 4:39 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 17/44] mm/pkeys: Introduce pks_mk_noaccess() ira.weiny
2022-01-27 17:54 ` [PATCH V8 18/44] x86/fault: Add a PKS test fault hook ira.weiny
2022-01-31 19:56 ` Edgecombe, Rick P
2022-02-11 20:40 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 19/44] mm/pkeys: PKS Testing, add pks_mk_*() tests ira.weiny
2022-02-01 17:45 ` Dave Hansen
2022-02-18 5:34 ` Ira Weiny
2022-02-18 15:28 ` Dave Hansen
2022-02-18 17:25 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 20/44] mm/pkeys: Add PKS test for context switching ira.weiny
2022-02-01 17:43 ` Edgecombe, Rick P
2022-02-22 21:42 ` Ira Weiny
2022-02-01 17:47 ` Edgecombe, Rick P
2022-02-01 19:52 ` Edgecombe, Rick P
2022-02-18 6:03 ` Ira Weiny
2022-02-18 6:02 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 21/44] x86/entry: Add auxiliary pt_regs space ira.weiny
2022-01-27 17:54 ` [PATCH V8 22/44] entry: Pass pt_regs to irqentry_exit_cond_resched() ira.weiny
2022-01-27 17:54 ` [PATCH V8 23/44] entry: Add architecture auxiliary pt_regs save/restore calls ira.weiny
2022-01-27 17:54 ` [PATCH V8 24/44] x86/entry: Define arch_{save|restore}_auxiliary_pt_regs() ira.weiny
2022-01-27 17:54 ` [PATCH V8 25/44] x86/pkeys: Preserve PKRS MSR across exceptions ira.weiny
2022-01-27 17:54 ` [PATCH V8 26/44] x86/fault: Print PKS MSR on fault ira.weiny
2022-02-01 18:13 ` Edgecombe, Rick P
2022-02-18 6:01 ` Ira Weiny
2022-02-18 17:28 ` Edgecombe, Rick P
2022-02-18 20:20 ` Dave Hansen
2022-02-18 20:54 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 27/44] mm/pkeys: Add PKS exception test ira.weiny
2022-01-27 17:54 ` [PATCH V8 28/44] mm/pkeys: Introduce pks_update_exception() ira.weiny
2022-01-27 17:54 ` [PATCH V8 29/44] mm/pkeys: Introduce PKS fault callbacks ira.weiny
2022-01-27 17:54 ` [PATCH V8 30/44] mm/pkeys: Test setting a PKS key in a custom fault callback ira.weiny
2022-02-01 0:55 ` Edgecombe, Rick P
2022-03-01 15:39 ` Ira Weiny
2022-02-01 17:42 ` Edgecombe, Rick P
2022-02-11 20:44 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 31/44] mm/pkeys: Add pks_available() ira.weiny
2022-01-27 17:54 ` [PATCH V8 32/44] memremap_pages: Add Kconfig for DEVMAP_ACCESS_PROTECTION ira.weiny
2022-02-04 15:49 ` Dan Williams
2022-01-27 17:54 ` [PATCH V8 33/44] memremap_pages: Introduce pgmap_protection_available() ira.weiny
2022-02-04 16:19 ` Dan Williams
2022-02-28 16:59 ` Ira Weiny
2022-03-01 15:56 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 34/44] memremap_pages: Introduce a PGMAP_PROTECTION flag ira.weiny
2022-01-27 17:54 ` [PATCH V8 35/44] memremap_pages: Introduce devmap_protected() ira.weiny
2022-01-27 17:54 ` [PATCH V8 36/44] memremap_pages: Reserve a PKS PKey for eventual use by PMEM ira.weiny
2022-02-01 18:35 ` Edgecombe, Rick P
2022-02-04 17:12 ` Dan Williams
2022-02-05 5:40 ` Ira Weiny
2022-02-05 8:19 ` Dan Williams
2022-02-06 18:14 ` Dan Williams
2022-02-08 22:48 ` Ira Weiny
2022-02-08 23:22 ` Dan Williams
2022-02-08 23:42 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 37/44] memremap_pages: Set PKS PKey in PTEs if PGMAP_PROTECTIONS is requested ira.weiny
2022-02-04 17:41 ` Dan Williams
2022-03-01 18:15 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 38/44] memremap_pages: Define pgmap_mk_{readwrite|noaccess}() calls ira.weiny
2022-02-04 18:35 ` Dan Williams
2022-02-05 0:09 ` Ira Weiny
2022-02-05 0:19 ` Dan Williams
2022-02-05 0:25 ` Dan Williams
2022-02-05 0:27 ` Dan Williams
2022-02-05 5:55 ` Ira Weiny
2022-02-05 6:28 ` Dan Williams
2022-02-22 22:05 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 39/44] memremap_pages: Add memremap.pks_fault_mode ira.weiny
2022-02-01 1:16 ` Edgecombe, Rick P
2022-03-02 0:20 ` Ira Weiny
2022-02-04 19:01 ` Dan Williams
2022-03-02 2:00 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 40/44] memremap_pages: Add pgmap_protection_flag_invalid() ira.weiny
2022-02-01 1:37 ` Edgecombe, Rick P
2022-03-02 2:01 ` Ira Weiny
2022-02-04 19:18 ` Dan Williams
2022-01-27 17:55 ` [PATCH V8 41/44] kmap: Ensure kmap works for devmap pages ira.weiny
2022-02-04 21:07 ` Dan Williams
2022-03-01 19:45 ` Ira Weiny
2022-03-01 19:50 ` Ira Weiny
2022-03-01 20:05 ` Dan Williams
2022-03-01 23:03 ` Ira Weiny [this message]
2022-01-27 17:55 ` [PATCH V8 42/44] dax: Stray access protection for dax_direct_access() ira.weiny
2022-02-04 5:19 ` Dan Williams
2022-03-01 18:13 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 43/44] nvdimm/pmem: Enable stray access protection ira.weiny
2022-02-04 21:10 ` Dan Williams
2022-03-01 18:18 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 44/44] devdax: " ira.weiny
2022-02-04 21:12 ` Dan Williams
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