From: Andrey Konovalov <andreyknvl@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: andrey.konovalov@linux.dev, Marco Elver <elver@google.com>,
Alexander Potapenko <glider@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Dmitry Vyukov <dvyukov@google.com>,
Andrey Ryabinin <ryabinin.a.a@gmail.com>,
kasan-dev <kasan-dev@googlegroups.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Sami Tolvanen <samitolvanen@google.com>,
Peter Collingbourne <pcc@google.com>,
Evgenii Stepanov <eugenis@google.com>,
Florian Mayer <fmayer@google.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH v2 2/4] arm64, scs: save scs_sp values per-cpu when switching stacks
Date: Tue, 5 Apr 2022 17:22:19 +0200 [thread overview]
Message-ID: <CA+fCnZekoAMEcS+0905JzP=Gu81R_F_em5Un8JL+FOF2Jj3rqg@mail.gmail.com> (raw)
In-Reply-To: <YkVzTbafttTHWETU@FVFF77S0Q05N>
On Thu, Mar 31, 2022 at 11:24 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Wed, Mar 23, 2022 at 04:32:53PM +0100, andrey.konovalov@linux.dev wrote:
> > From: Andrey Konovalov <andreyknvl@google.com>
> >
> > Instead of trying to retrieve the SCS pointers from the stack, change
> > interrupt handlers (for hard IRQ, Normal and Critical SDEI) to save the
> > previous SCS pointer in a per-CPU variable.
>
> I'm *really* not keen on *always* poking this in the entry code for the
> uncommon case of unwind. It complicates the entry code and means we're always
> paying a cost for potentially no benefit. At a high-level, I don't think this
> is the right approach.
This also gives a 5% slowdown, which is not acceptable.
What we can do instead, is to not collect frames from the higher
exception levels at all. This would leave SCS-based stack collection
method impaired, but this is probably fine for KASAN's use case:
currently, stack depot filters out higher-level frames anyway, so
KASAN never saves them. And the lower-level part of the stack trace is
enough to identify the allocation.
Thanks!
> For the regular unwinder, I want to rework things such that we can identify
> exception boundaries and look into the regs (e.g. so that we can recover the
> PC+LR+FP and avoid duplicating part of this in a frame record), and I'd much
> prefer that we did the same here.
next prev parent reply other threads:[~2022-04-06 1:53 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-23 15:32 [PATCH v2 0/4] kasan, arm64, scs, stacktrace: collect stack traces from Shadow Call Stack andrey.konovalov
2022-03-23 15:32 ` [PATCH v2 1/4] stacktrace: add interface based on shadow call stack andrey.konovalov
2022-03-25 20:46 ` Andrew Morton
2022-03-29 18:36 ` Andrey Konovalov
2022-03-31 9:19 ` Mark Rutland
2022-04-05 15:37 ` Andrey Konovalov
2022-03-23 15:32 ` [PATCH v2 2/4] arm64, scs: save scs_sp values per-cpu when switching stacks andrey.konovalov
2022-03-24 11:08 ` kernel test robot
2022-03-24 21:39 ` kernel test robot
2022-03-31 9:24 ` Mark Rutland
2022-04-05 15:22 ` Andrey Konovalov [this message]
2022-03-23 15:32 ` [PATCH v2 3/4] arm64: implement stack_trace_save_shadow andrey.konovalov
2022-03-24 8:35 ` kernel test robot
2022-03-31 9:32 ` Mark Rutland
2022-04-05 15:38 ` Andrey Konovalov
2022-03-23 15:32 ` [PATCH v2 4/4] kasan: use stack_trace_save_shadow andrey.konovalov
2022-03-28 12:49 ` Marco Elver
2022-03-29 18:36 ` Andrey Konovalov
2022-03-28 12:36 ` [PATCH v2 0/4] kasan, arm64, scs, stacktrace: collect stack traces from Shadow Call Stack Marco Elver
2022-03-29 18:36 ` Andrey Konovalov
2022-03-29 20:11 ` Andrey Konovalov
2022-03-31 9:54 ` Mark Rutland
2022-03-31 12:39 ` Mark Rutland
2022-04-05 15:10 ` Andrey Konovalov
2022-04-07 18:41 ` Mark Rutland
2022-04-13 19:28 ` Andrey Konovalov
2022-04-14 7:02 ` Mark Rutland
2022-04-05 15:09 ` Andrey Konovalov
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