From: Ira Weiny <ira.weiny@intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Fenghua Yu <fenghua.yu@intel.com>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
linux-nvdimm <linux-nvdimm@lists.01.org>,
Linux-MM <linux-mm@kvack.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [PATCH V3.1] entry: Pass irqentry_state_t by reference
Date: Wed, 16 Dec 2020 16:38:36 -0800 [thread overview]
Message-ID: <20201217003835.GZ1563847@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <CALCETrWoh5BYnU16adT7i6tsQ77PGaLN_qyZnCy-WfO3UJoykw@mail.gmail.com>
On Tue, Dec 15, 2020 at 06:09:02PM -0800, Andy Lutomirski wrote:
> On Tue, Dec 15, 2020 at 5:32 PM Ira Weiny <ira.weiny@intel.com> wrote:
> >
> > On Fri, Dec 11, 2020 at 02:14:28PM -0800, Andy Lutomirski wrote:
> > > On Mon, Nov 23, 2020 at 10:10 PM <ira.weiny@intel.com> wrote:
>
> > > IOW we have:
> > >
> > > struct extended_pt_regs {
> > > bool rcu_whatever;
> > > other generic fields here;
> > > struct arch_extended_pt_regs arch_regs;
> > > struct pt_regs regs;
> > > };
> > >
> > > and arch_extended_pt_regs has unsigned long pks;
> > >
> > > and instead of passing a pointer to irqentry_state_t to the generic
> > > entry/exit code, we just pass a pt_regs pointer. And we have a little
> > > accessor like:
> > >
> > > struct extended_pt_regs *extended_regs(struct pt_regs *) { return
> > > container_of(...); }
> > >
> > > And we tell eBPF that extended_pt_regs is NOT ABI, and we will change
> > > it whenever we feel like just to keep you on your toes, thank you very
> > > much.
> > >
> > > Does this seem reasonable?
> >
> > Conceptually yes. But I'm failing to see how this implementation can be made
> > generic for the generic fields. The pks fields, assuming they stay x86
> > specific, would be reasonable to add in PUSH_AND_CLEAR_REGS. But the
> > rcu/lockdep field is generic. Wouldn't we have to modify every architecture to
> > add space for the rcu/lockdep bool?
> >
> > If not, where is a generic place that could be done? Basically I'm missing how
> > the effective stack structure can look like this:
> >
> > > struct extended_pt_regs {
> > > bool rcu_whatever;
> > > other generic fields here;
> > > struct arch_extended_pt_regs arch_regs;
> > > struct pt_regs regs;
> > > };
> >
> > It seems more reasonable to make it look like:
> >
> > #ifdef CONFIG_ARCH_HAS_SUPERVISOR_PKEYS
> > struct extended_pt_regs {
> > unsigned long pkrs;
> > struct pt_regs regs;
> > };
> > #endif
> >
> > And leave the rcu/lockdep bool passed by value as before (still in C).
>
> We could certainly do this,
I'm going to start with this basic support. Because I have 0 experience in
most of these architectures.
> but we could also allocate some generic
> space. PUSH_AND_CLEAR_REGS would get an extra instruction like:
>
> subq %rsp, $GENERIC_PTREGS_SIZE
>
> or however this should be written. That field would be defined in
> asm-offsets.c. And yes, all the generic-entry architectures would
> need to get onboard.
What do you mean by 'generic-entry' architectures? I thought they all used the
generic entry code?
Regardless I would need to start another thread on this topic with any of those
architecture maintainers to see what the work load would be for this. I don't
think I can do it on my own.
FWIW I think it is a bit unfair to hold up the PKS support in x86 for making
these generic fields part of the stack frame. So perhaps that could be made a
follow on to the PKS series?
>
> If we wanted to be fancy, we could split the generic area into
> initialize-to-zero and uninitialized for debugging purposes, but that
> might be more complication than is worthwhile.
Ok, agreed, but this is step 3 or 4 at the earliest.
Ira
next prev parent reply other threads:[~2020-12-17 0:39 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-06 23:28 [PATCH V3 00/10] PKS: Add Protection Keys Supervisor (PKS) support V3 ira.weiny
2020-11-06 23:28 ` [PATCH V3 01/10] x86/pkeys: Create pkeys_common.h ira.weiny
2020-11-06 23:29 ` [PATCH V3 02/10] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support ira.weiny
2020-11-06 23:29 ` [PATCH V3 03/10] x86/pks: Add PKS defines and Kconfig options ira.weiny
2020-11-06 23:29 ` [PATCH V3 04/10] x86/pks: Preserve the PKRS MSR on context switch ira.weiny
2020-12-17 14:50 ` Thomas Gleixner
2020-12-17 22:43 ` Thomas Gleixner
2020-12-18 13:57 ` Thomas Gleixner
2020-12-18 19:20 ` Dan Williams
2020-12-18 21:06 ` Thomas Gleixner
2020-12-18 21:58 ` Dan Williams
2020-12-18 22:44 ` Thomas Gleixner
2020-12-18 19:42 ` Ira Weiny
2020-12-18 20:10 ` Dave Hansen
2020-12-18 21:30 ` Thomas Gleixner
2020-12-18 4:05 ` Ira Weiny
2020-12-17 20:41 ` [NEEDS-REVIEW] " Dave Hansen
2020-12-18 4:10 ` Ira Weiny
2020-12-18 15:33 ` Dave Hansen
2020-11-06 23:29 ` [PATCH V3 05/10] x86/entry: Pass irqentry_state_t by reference ira.weiny
2020-11-15 18:58 ` Thomas Gleixner
2020-11-16 18:49 ` Ira Weiny
2020-11-16 20:36 ` Thomas Gleixner
2020-11-24 6:09 ` [PATCH V3.1] entry: " ira.weiny
2020-12-11 22:14 ` Andy Lutomirski
2020-12-16 1:32 ` Ira Weiny
2020-12-16 2:09 ` Andy Lutomirski
2020-12-17 0:38 ` Ira Weiny [this message]
2020-12-17 13:07 ` Thomas Gleixner
2020-12-17 13:19 ` Peter Zijlstra
2020-12-17 15:35 ` Andy Lutomirski
2020-12-17 16:58 ` Thomas Gleixner
2020-11-06 23:29 ` [PATCH V3 06/10] x86/entry: Preserve PKRS MSR across exceptions ira.weiny
2020-12-17 15:28 ` Thomas Gleixner
2020-11-06 23:29 ` [PATCH V3 07/10] x86/fault: Report the PKRS state on fault ira.weiny
2020-11-06 23:29 ` [PATCH V3 08/10] x86/pks: Add PKS kernel API ira.weiny
2020-12-23 20:39 ` Randy Dunlap
2020-11-06 23:29 ` [PATCH V3 09/10] x86/pks: Enable Protection Keys Supervisor (PKS) ira.weiny
2020-11-06 23:29 ` [PATCH V3 10/10] x86/pks: Add PKS test code ira.weiny
2020-12-17 20:55 ` Dave Hansen
2020-12-18 4:05 ` Ira Weiny
2020-12-18 16:59 ` Dan Williams
2020-12-07 22:14 ` [PATCH V3 00/10] PKS: Add Protection Keys Supervisor (PKS) support V3 Ira Weiny
2020-12-08 15:55 ` Thomas Gleixner
2020-12-08 17:22 ` Ira Weiny
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