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Message-ID: <41ac24c4-6c95-d946-2679-c1be2cb20536@intel.com>
Date:   Thu, 17 Nov 2022 15:54:21 -0800
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Subject: Re: WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/kfence.h:46
 kfence_protect
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To:     Marco Elver <elver@google.com>
Cc:     Naresh Kamboju <naresh.kamboju@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>,
        kasan-dev <kasan-dev@googlegroups.com>, X86 ML <x86@kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, regressions@lists.linux.dev,
        lkft-triage@lists.linaro.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>
References: <CA+G9fYuFxZTxkeS35VTZMXwQvohu73W3xbZ5NtjebsVvH6hCuA@mail.gmail.com>
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 <4208866d-338f-4781-7ff9-023f016c5b07@intel.com>
 <Y3bCV6VckVUEF7Pq@elver.google.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <Y3bCV6VckVUEF7Pq@elver.google.com>
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On 11/17/22 15:23, Marco Elver wrote:
> Yes - it's the 'level != PG_LEVEL_4K'.

That plus the bisect made it pretty easy to find, thanks for the effort!

Could you double-check that the attached patch fixes it?  It seemed to
for me.

The issue was that the new "No changes, easy!" check in the suspect
commit didn't check the cpa->force_split option.  It didn't split down
to 4k and then all hell broke loose.

Oh, and I totally misread the kfence ability to tolerate partial TLB
flushes.  Sorry for the noise there!

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