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Date: Thu, 17 Jan 2019 08:14:41 -0700
From: Khalid Aziz <khalid.aziz@...cle.com>
To: Laura Abbott <labbott@...hat.com>, juergh@...il.com, tycho@...ho.ws,
jsteckli@...zon.de, ak@...ux.intel.com, torvalds@...ux-foundation.org,
liran.alon@...cle.com, keescook@...gle.com, konrad.wilk@...cle.com
Cc: deepa.srinivasan@...cle.com, chris.hyser@...cle.com, tyhicks@...onical.com,
dwmw@...zon.co.uk, andrew.cooper3@...rix.com, jcm@...hat.com,
boris.ostrovsky@...cle.com, kanth.ghatraju@...cle.com,
joao.m.martins@...cle.com, jmattson@...gle.com,
pradeep.vincent@...cle.com, john.haxby@...cle.com, tglx@...utronix.de,
kirill.shutemov@...ux.intel.com, hch@....de, steven.sistare@...cle.com,
kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, x86@...nel.org,
"Vasileios P . Kemerlis" <vpk@...columbia.edu>,
Juerg Haefliger <juerg.haefliger@...onical.com>,
Tycho Andersen <tycho@...ker.com>,
Marco Benatto <marco.antonio.780@...il.com>,
David Woodhouse <dwmw2@...radead.org>
Subject: Re: [RFC PATCH v7 14/16] EXPERIMENTAL: xpfo, mm: optimize spin lock
usage in xpfo_kmap
On 1/16/19 5:18 PM, Laura Abbott wrote:
> On 1/10/19 1:09 PM, Khalid Aziz wrote:
>> From: Julian Stecklina <jsteckli@...zon.de>
>>
>> We can reduce spin lock usage in xpfo_kmap to the 0->1 transition of
>> the mapcount. This means that xpfo_kmap() can now race and that we
>> get spurious page faults.
>>
>> The page fault handler helps the system make forward progress by
>> fixing the page table instead of allowing repeated page faults until
>> the right xpfo_kmap went through.
>>
>> Model-checked with up to 4 concurrent callers with Spin.
>>
>
> This needs the spurious check for arm64 as well. This at
> least gets me booting but could probably use more review:
>
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 7d9571f4ae3d..8f425848cbb9 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -32,6 +32,7 @@
> #include <linux/perf_event.h>
> #include <linux/preempt.h>
> #include <linux/hugetlb.h>
> +#include <linux/xpfo.h>
>
> #include <asm/bug.h>
> #include <asm/cmpxchg.h>
> @@ -289,6 +290,9 @@ static void __do_kernel_fault(unsigned long addr,
> unsigned int esr,
> if (!is_el1_instruction_abort(esr) && fixup_exception(regs))
> return;
>
> + if (xpfo_spurious_fault(addr))
> + return;
> +
> if (is_el1_permission_fault(addr, esr, regs)) {
> if (esr & ESR_ELx_WNR)
> msg = "write to read-only memory";
>
>
That makes sense. Thanks for debugging this. I will add this to patch 14
("EXPERIMENTAL: xpfo, mm: optimize spin lock usage in xpfo_kmap").
Thanks,
Khalid
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