From: Will Deacon <will@kernel.org>
To: "guanghui.fgh" <guanghuifeng@linux.alibaba.com>
Cc: baolin.wang@linux.alibaba.com, catalin.marinas@arm.com,
akpm@linux-foundation.org, david@redhat.com, jianyong.wu@arm.com,
james.morse@arm.com, quic_qiancai@quicinc.com,
christophe.leroy@csgroup.eu, jonathan@marek.ca,
mark.rutland@arm.com, thunder.leizhen@huawei.com,
anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, rppt@kernel.org,
geert+renesas@glider.be, ardb@kernel.org, linux-mm@kvack.org,
yaohongbo@linux.alibaba.com,
alikernel-developer@linux.alibaba.com
Subject: Re: [PATCH v5] arm64: mm: fix linear mem mapping access performance degradation
Date: Mon, 18 Jul 2022 14:10:06 +0100 [thread overview]
Message-ID: <20220718131005.GA12406@willie-the-truck> (raw)
In-Reply-To: <a6caa7b5-6a15-987d-c0a3-dcf9c1cdd3b0@linux.alibaba.com>
On Sun, Jul 10, 2022 at 11:33:02PM +0800, guanghui.fgh wrote:
> In short, this path work:
>
> 1.Before doing work for rebuiling crashkernel mem, the pgd is swapper_pg_dir
> in [[[ttbr1]]]
>
> 2.Change the [[[ttbr0]]]to use idmap_pg_dir pgd
>
> 3.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] are mapped [[[only]]]
> with idmap_pg_dir mapping in [[[ttbr0]]]
>
> 4.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] will flush tlb all,
> switch [[[ttbr1]]] to use init_pg_dir pgd(and flush tlb all again).
> There is no tlb conflict to swapper_pg_dir.
> There is no tlb cache for swapper_pg_dir.
>
> 5.Woring with init_pg_dir pgd to access swapper_pg_dir pagetable with fix
> mapping. And modify crashkernel mapping in the swapper_pg_dir without any
> tlb conflict and flush.
>
> 6.When finishing the work, switch ttbr1 pgd to the origin swapper_pg_dir
> with cpu_replace_ttbr1 function(similar to the above).
I do not think that this complexity is justified. As I have stated on
numerous occasions already, I would prefer that we leave the crashkernel
mapped when rodata is not "full". That fixes your performance issue and
matches what we do for module code, so I do not see a security argument
against it.
I do not plan to merge this patch as-is.
Thanks,
Will
WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: "guanghui.fgh" <guanghuifeng@linux.alibaba.com>
Cc: baolin.wang@linux.alibaba.com, catalin.marinas@arm.com,
akpm@linux-foundation.org, david@redhat.com, jianyong.wu@arm.com,
james.morse@arm.com, quic_qiancai@quicinc.com,
christophe.leroy@csgroup.eu, jonathan@marek.ca,
mark.rutland@arm.com, thunder.leizhen@huawei.com,
anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, rppt@kernel.org,
geert+renesas@glider.be, ardb@kernel.org, linux-mm@kvack.org,
yaohongbo@linux.alibaba.com,
alikernel-developer@linux.alibaba.com
Subject: Re: [PATCH v5] arm64: mm: fix linear mem mapping access performance degradation
Date: Mon, 18 Jul 2022 14:10:06 +0100 [thread overview]
Message-ID: <20220718131005.GA12406@willie-the-truck> (raw)
In-Reply-To: <a6caa7b5-6a15-987d-c0a3-dcf9c1cdd3b0@linux.alibaba.com>
On Sun, Jul 10, 2022 at 11:33:02PM +0800, guanghui.fgh wrote:
> In short, this path work:
>
> 1.Before doing work for rebuiling crashkernel mem, the pgd is swapper_pg_dir
> in [[[ttbr1]]]
>
> 2.Change the [[[ttbr0]]]to use idmap_pg_dir pgd
>
> 3.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] are mapped [[[only]]]
> with idmap_pg_dir mapping in [[[ttbr0]]]
>
> 4.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] will flush tlb all,
> switch [[[ttbr1]]] to use init_pg_dir pgd(and flush tlb all again).
> There is no tlb conflict to swapper_pg_dir.
> There is no tlb cache for swapper_pg_dir.
>
> 5.Woring with init_pg_dir pgd to access swapper_pg_dir pagetable with fix
> mapping. And modify crashkernel mapping in the swapper_pg_dir without any
> tlb conflict and flush.
>
> 6.When finishing the work, switch ttbr1 pgd to the origin swapper_pg_dir
> with cpu_replace_ttbr1 function(similar to the above).
I do not think that this complexity is justified. As I have stated on
numerous occasions already, I would prefer that we leave the crashkernel
mapped when rodata is not "full". That fixes your performance issue and
matches what we do for module code, so I do not see a security argument
against it.
I do not plan to merge this patch as-is.
Thanks,
Will
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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-07-18 13:10 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-02 15:57 [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation Guanghui Feng
2022-07-02 15:57 ` Guanghui Feng
2022-07-04 10:35 ` Will Deacon
2022-07-04 10:35 ` Will Deacon
2022-07-04 10:58 ` guanghui.fgh
2022-07-04 10:58 ` guanghui.fgh
2022-07-04 11:14 ` Will Deacon
2022-07-04 11:14 ` Will Deacon
2022-07-04 12:05 ` guanghui.fgh
2022-07-04 12:05 ` guanghui.fgh
2022-07-04 13:15 ` Will Deacon
2022-07-04 13:15 ` Will Deacon
2022-07-04 13:41 ` guanghui.fgh
2022-07-04 13:41 ` guanghui.fgh
2022-07-04 14:11 ` guanghui.fgh
2022-07-04 14:11 ` guanghui.fgh
2022-07-04 14:23 ` Will Deacon
2022-07-04 14:23 ` Will Deacon
2022-07-04 14:34 ` guanghui.fgh
2022-07-04 14:34 ` guanghui.fgh
2022-07-04 16:38 ` Will Deacon
2022-07-04 16:38 ` Will Deacon
2022-07-04 17:09 ` Ard Biesheuvel
2022-07-04 17:09 ` Ard Biesheuvel
2022-07-05 8:35 ` Baoquan He
2022-07-05 8:35 ` Baoquan He
2022-07-05 8:35 ` Baoquan He
2022-07-05 9:52 ` Will Deacon
2022-07-05 9:52 ` Will Deacon
2022-07-05 12:07 ` guanghui.fgh
2022-07-05 12:07 ` guanghui.fgh
2022-07-05 12:11 ` Will Deacon
2022-07-05 12:11 ` Will Deacon
2022-07-05 12:27 ` guanghui.fgh
2022-07-05 12:27 ` guanghui.fgh
2022-07-05 12:56 ` Mike Rapoport
2022-07-05 12:56 ` Mike Rapoport
2022-07-05 13:17 ` guanghui.fgh
2022-07-05 13:17 ` guanghui.fgh
2022-07-05 15:02 ` Mike Rapoport
2022-07-05 15:02 ` Mike Rapoport
2022-07-05 15:34 ` Catalin Marinas
2022-07-05 15:34 ` Catalin Marinas
2022-07-05 15:57 ` Mike Rapoport
2022-07-05 15:57 ` Mike Rapoport
2022-07-05 17:05 ` Catalin Marinas
2022-07-05 17:05 ` Catalin Marinas
2022-07-05 20:45 ` Mike Rapoport
2022-07-05 20:45 ` Mike Rapoport
2022-07-06 2:49 ` guanghui.fgh
2022-07-06 2:49 ` guanghui.fgh
2022-07-06 7:43 ` Catalin Marinas
2022-07-06 7:43 ` Catalin Marinas
2022-07-06 10:04 ` Catalin Marinas
2022-07-06 10:04 ` Catalin Marinas
2022-07-06 13:54 ` Mike Rapoport
2022-07-06 13:54 ` Mike Rapoport
2022-07-06 15:18 ` guanghui.fgh
2022-07-06 15:18 ` guanghui.fgh
2022-07-06 15:30 ` guanghui.fgh
2022-07-06 15:30 ` guanghui.fgh
2022-07-06 15:40 ` Catalin Marinas
2022-07-06 15:40 ` Catalin Marinas
2022-07-07 17:02 ` guanghui.fgh
2022-07-07 17:02 ` guanghui.fgh
2022-07-08 12:28 ` [PATCH RESEND " guanghui.fgh
2022-07-08 12:28 ` guanghui.fgh
2022-07-10 13:44 ` [PATCH v5] " Guanghui Feng
2022-07-10 13:44 ` Guanghui Feng
2022-07-10 14:32 ` guanghui.fgh
2022-07-10 14:32 ` guanghui.fgh
2022-07-10 15:33 ` guanghui.fgh
2022-07-10 15:33 ` guanghui.fgh
2022-07-18 13:10 ` Will Deacon [this message]
2022-07-18 13:10 ` Will Deacon
2022-07-25 6:46 ` Mike Rapoport
2022-07-25 6:46 ` Mike Rapoport
2022-07-05 2:44 ` [PATCH v4] " guanghui.fgh
2022-07-05 2:44 ` guanghui.fgh
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