From: Zhenhua Huang <quic_zhenhuah@quicinc.com>
To: Marco Elver <elver@google.com>
Cc: <catalin.marinas@arm.com>, <will@kernel.org>, <glider@google.com>,
<akpm@linux-foundation.org>,
<linux-arm-kernel@lists.infradead.org>, <linux-mm@kvack.org>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH] mm: kfence: export kfence_enabled as global variables
Date: Tue, 7 Feb 2023 15:46:53 +0800 [thread overview]
Message-ID: <b223194c-63b3-d2eb-d450-10550bd12998@quicinc.com> (raw)
In-Reply-To: <CANpmjNP0tgPhCWS4dE4_VbvyTk-9qhQiM3oWDtJogAPQXtbXVA@mail.gmail.com>
Thanks Marco!
On 2023/2/7 15:19, Marco Elver wrote:
> On Tue, 7 Feb 2023 at 07:15, Zhenhua Huang <quic_zhenhuah@quicinc.com> wrote:
>>
>> Export the variable to ease the judgement of whether kfence enabled
>> at runtime. It should be more precise than through kernel config
>> "CONFIG_KFENCE".
>>
>> For example We can disable kfence at runtime using bootargs
>> "kfence.sample_interval=0" but CONFIG_KFENCE enabled.
>> It was false positive.
>>
>> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
>> ---
>> arch/arm64/mm/pageattr.c | 3 ++-
>> include/linux/kfence.h | 2 ++
>> mm/kfence/core.c | 2 +-
>> 3 files changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>> index 79dd201..208d780 100644
>> --- a/arch/arm64/mm/pageattr.c
>> +++ b/arch/arm64/mm/pageattr.c
>> @@ -7,6 +7,7 @@
>> #include <linux/module.h>
>> #include <linux/sched.h>
>> #include <linux/vmalloc.h>
>> +#include <linux/kfence.h>
>>
>> #include <asm/cacheflush.h>
>> #include <asm/set_memory.h>
>> @@ -27,7 +28,7 @@ bool can_set_direct_map(void)
>> * protect/unprotect single pages.
>> */
>> return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
>> - IS_ENABLED(CONFIG_KFENCE);
>> + kfence_enabled;
>
> Unfortunately this won't work, because it's possible to enable KFENCE
> after the kernel has booted with e.g.: echo 100 >
> /sys/module/kfence/parameters/sample_interval
Yeah, got it. Thanks for catching it.
>
> What is the problem you have encountered? Is the page-granular direct
> map causing issues?
We're working on a low memory target, page-granular mapping costed more
(2M per 1GB) memory. Due to GKI constraints, it is not easy to disable
CONFIG_KFENCE. So my intention was to move the judgement to runtime
configurable w/ CONFIG_KFENCE on...
Do you have any further suggestion/proposal on this? Many Thanks!
Thanks,
Zhenhua
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next prev parent reply other threads:[~2023-02-07 7:48 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-07 6:15 [PATCH] mm: kfence: export kfence_enabled as global variables Zhenhua Huang
2023-02-07 7:19 ` Marco Elver
2023-02-07 7:46 ` Zhenhua Huang [this message]
2023-02-07 10:28 ` Alexander Potapenko
2023-02-07 10:42 ` Zhenhua Huang
2023-02-07 10:48 ` Mark Rutland
2023-02-07 12:35 ` Zhenhua Huang
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