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From: Christoph Hellwig <hch@infradead.org>
To: Anup Patel <anup@brainfault.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	Palmer Dabbelt <palmer@sifive.com>,
	Anup Patel <Anup.Patel@wdc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Atish Patra <Atish.Patra@wdc.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>
Subject: Re: [PATCH v3 4/4] RISC-V: Allow booting kernel from any 4KB aligned address
Date: Wed, 27 Mar 2019 00:54:41 -0700	[thread overview]
Message-ID: <20190327075441.GA29894@infradead.org> (raw)
In-Reply-To: <CAAhSdy2je-_=AHPawbV-8cUR0P7WvqDZ5wNdEmDVQkR-a88Eog@mail.gmail.com>

On Mon, Mar 25, 2019 at 09:46:59PM +0530, Anup Patel wrote:
> > Why do you even care about kernel mappings for non-existant ram.
> 
> We care because there will always be some buggy kernel driver/code going
> out-of-bound and accessing non-existent RAM. If we by default map all
> possible kernel virtual address then behaviour of buggy accesses will be
> unpredictable.
> 
> Further, I think we should also make .text and .rodata sections of kernel
> as read-only. This will protect kernel code and rodata.

All of that is useful at the final_setup_vm() time - but none of it
matters during early setup_vm where life is complicated.

Mike suggested on the previous iteration that you only do smaller
mappings when setting up the final mapping to avoid the ops churn,
and I fully agree with him. 

So I would suggest we avoid complicated the fiddly early boot changes
that just add complxity, and you instead redirect your efforts to
say implemented proper ro and non-executable sections using 4k mappings
in the final VM setup only.  That should actuall lead to less code
and complexity, and provide more benefits.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Anup Patel <anup@brainfault.org>
Cc: Palmer Dabbelt <palmer@sifive.com>,
	Anup Patel <Anup.Patel@wdc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Christoph Hellwig <hch@infradead.org>,
	Atish Patra <Atish.Patra@wdc.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>
Subject: Re: [PATCH v3 4/4] RISC-V: Allow booting kernel from any 4KB aligned address
Date: Wed, 27 Mar 2019 00:54:41 -0700	[thread overview]
Message-ID: <20190327075441.GA29894@infradead.org> (raw)
In-Reply-To: <CAAhSdy2je-_=AHPawbV-8cUR0P7WvqDZ5wNdEmDVQkR-a88Eog@mail.gmail.com>

On Mon, Mar 25, 2019 at 09:46:59PM +0530, Anup Patel wrote:
> > Why do you even care about kernel mappings for non-existant ram.
> 
> We care because there will always be some buggy kernel driver/code going
> out-of-bound and accessing non-existent RAM. If we by default map all
> possible kernel virtual address then behaviour of buggy accesses will be
> unpredictable.
> 
> Further, I think we should also make .text and .rodata sections of kernel
> as read-only. This will protect kernel code and rodata.

All of that is useful at the final_setup_vm() time - but none of it
matters during early setup_vm where life is complicated.

Mike suggested on the previous iteration that you only do smaller
mappings when setting up the final mapping to avoid the ops churn,
and I fully agree with him. 

So I would suggest we avoid complicated the fiddly early boot changes
that just add complxity, and you instead redirect your efforts to
say implemented proper ro and non-executable sections using 4k mappings
in the final VM setup only.  That should actuall lead to less code
and complexity, and provide more benefits.

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  parent reply	other threads:[~2019-03-27  7:54 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-25  9:22 [PATCH v3 0/4] Boot RISC-V kernel from any 4KB aligned address Anup Patel
2019-03-25  9:22 ` Anup Patel
2019-03-25  9:23 ` [PATCH v3 1/4] RISC-V: Add separate defconfig for 32bit systems Anup Patel
2019-03-25  9:23   ` Anup Patel
2019-03-25  9:23 ` [PATCH v3 2/4] RISC-V: Fix memory reservation in setup_bootmem() Anup Patel
2019-03-25  9:23   ` Anup Patel
2019-03-25 11:38   ` Christoph Hellwig
2019-03-25 11:38     ` Christoph Hellwig
2019-03-25 16:13   ` Mike Rapoport
2019-03-25 16:13     ` Mike Rapoport
2019-04-24 21:06   ` Palmer Dabbelt
2019-04-24 21:06     ` Palmer Dabbelt
2019-03-25  9:23 ` [PATCH v3 3/4] RISC-V: Remove redundant trampoline page table Anup Patel
2019-03-25  9:23   ` Anup Patel
2019-03-25 11:38   ` Christoph Hellwig
2019-03-25 11:38     ` Christoph Hellwig
2019-03-25  9:23 ` [PATCH v3 4/4] RISC-V: Allow booting kernel from any 4KB aligned address Anup Patel
2019-03-25  9:23   ` Anup Patel
2019-03-25 11:39   ` Christoph Hellwig
2019-03-25 11:39     ` Christoph Hellwig
2019-03-25 12:42     ` Anup Patel
2019-03-25 12:42       ` Anup Patel
2019-03-25 14:55       ` Christoph Hellwig
2019-03-25 14:55         ` Christoph Hellwig
2019-03-25 12:48     ` Anup Patel
2019-03-25 12:48       ` Anup Patel
2019-03-25 14:59       ` Christoph Hellwig
2019-03-25 14:59         ` Christoph Hellwig
2019-03-25 16:16         ` Anup Patel
2019-03-25 16:16           ` Anup Patel
2019-03-25 17:35           ` Gary Guo
2019-03-26  9:43             ` Anup Patel
2019-03-27  7:54           ` Christoph Hellwig [this message]
2019-03-27  7:54             ` Christoph Hellwig
2019-03-28  7:55             ` Mike Rapoport
2019-03-28  7:55               ` Mike Rapoport
2019-03-28  9:52               ` Anup Patel
2019-03-28  9:52                 ` Anup Patel
2019-03-28 10:24                 ` Anup Patel
2019-03-28 10:24                   ` Anup Patel
2019-03-28 15:35 Anthony Coulter
2019-03-28 15:35 ` Anthony Coulter

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