From: Mike Rapoport <rppt@linux.ibm.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Palmer Dabbelt <palmer@sifive.com>,
Anup Patel <anup@brainfault.org>, Anup Patel <Anup.Patel@wdc.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.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: Thu, 28 Mar 2019 09:55:26 +0200 [thread overview]
Message-ID: <20190328075526.GC14864@rapoport-lnx> (raw)
In-Reply-To: <20190327075441.GA29894@infradead.org>
On Wed, Mar 27, 2019 at 12:54:41AM -0700, Christoph Hellwig wrote:
> 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.
It might be worth keeping trampoline_pg_dir if we are to split setup_vm().
Then setup_vm() will only initialize the trampoline_pg_dir and
final_setup_vm() will setup the swapper_pg_dir and switch to it.
Otherwise final_setup_vm() would need to update live mappings which might
be fragile.
--
Sincerely yours,
Mike.
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next prev parent reply other threads:[~2019-03-28 7:55 UTC|newest]
Thread overview: 22+ 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 9:23 ` [PATCH v3 1/4] RISC-V: Add separate defconfig for 32bit systems Anup Patel
2019-03-25 9:23 ` [PATCH v3 2/4] RISC-V: Fix memory reservation in setup_bootmem() Anup Patel
2019-03-25 11:38 ` Christoph Hellwig
2019-03-25 16:13 ` Mike Rapoport
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 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 11:39 ` Christoph Hellwig
2019-03-25 12:42 ` Anup Patel
2019-03-25 14:55 ` Christoph Hellwig
2019-03-25 12:48 ` Anup Patel
2019-03-25 14:59 ` Christoph Hellwig
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
2019-03-28 7:55 ` Mike Rapoport [this message]
2019-03-28 9:52 ` Anup Patel
2019-03-28 10:24 ` Anup Patel
2019-03-28 15:35 Anthony Coulter
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