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

From: Dayeol Lee
Subject: Re: [PATCH] target/riscv: PMP violation due to wrong size parameter
Date: Mon, 7 Oct 2019 10:19:18 -0700

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?


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 <address@hidden> 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

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.


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