Re: [PATCH] target/riscv: PMP violation due to wrong size parameter

From: Dayeol Lee <dayeol@berkeley.edu>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: "open list:RISC-V TCG CPUs" <qemu-riscv@nongnu.org>,
	Sagar Karandikar <sagark@eecs.berkeley.edu>,
	Bastian Koppelmann <kbastian@mail.uni-paderborn.de>,
	Palmer Dabbelt <palmer@sifive.com>,
	qemu-devel@nongnu.org,
	Alistair Francis <Alistair.Francis@wdc.com>
Subject: Re: [PATCH] target/riscv: PMP violation due to wrong size parameter
Date: Mon, 7 Oct 2019 10:19:18 -0700	[thread overview]
Message-ID: <CACjxMEsw+Deh176JLP2aF4Pdkb_s8MiPApwMON-_K6ed61-Zyw@mail.gmail.com> (raw)
In-Reply-To: <5583387c-5c5b-8890-999b-2ba4d75cd69d@linaro.org>

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Thank you very much for the clarification!

I found tlb_set_page with size != TARGET_PAGE_SIZE makes the translation
way too slow; the Linux doesn't seem to boot.

If that's the only way to reduce PMP granularity to less than
TARGET_PAGE_SIZE,
Can we just set the PMP default granularity to TARGET_PAGE_SIZE as it did
before?

OR

Can we bypass the partial match violation when size is unknown? (check the
starting address only)

I think both of the options does not exactly match with the ISA
specification,
but given that size=0 always causes the problem, I want it to be fixed as
soon as possible.

Any thoughts would be appreciated!

On Mon, Oct 7, 2019, 6:00 AM Richard Henderson <richard.henderson@linaro.org>
wrote:

> On 10/6/19 10:28 PM, Dayeol Lee wrote:
> > riscv_cpu_tlb_fill() uses the `size` parameter to check PMP violation
> > using pmp_hart_has_privs().
> > However, the size passed from tlb_fill(), which is called by
> > get_page_addr_code(), is always a hard-coded value 0.
> > This causes a false PMP violation if the instruction presents on a
> > PMP boundary.
> >
> > In order to fix, simply correct the size to 4 if the access_type is
> > MMU_INST_FETCH.
>
> That's not correct.
>
> In general, size 0 means "unknown size".  In this case, the one tlb lookup
> is
> going to be used by lots of instructions -- everything that fits on the
> page.
>
> If you want to support PMP on things that are not page boundaries, then you
> will also have to call tlb_set_page with size != TARGET_PAGE_SIZE.
>
> Fixing that will cause instructions within that page to be executed one at
> a
> time, which also means they will be tlb_fill'd one at a time, which means
> that
> you'll get the correct size value.
>
> Which will be 2 or 4, depending on whether the configuration supports the
> Compressed extension, and not just 4.
>
>
> r~
>

>

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