linux-kernel - Re: [PATCH] riscv: Don't use va_pa

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Message-ID: <ae122f06f0de1075cf266b639ce36da3@mailhost.ics.forth.gr>
Date:   Sat, 09 Oct 2021 16:18:48 +0300
From:   Nick Kossifidis <mick@....forth.gr>
To:     Alexandre Ghiti <alexandre.ghiti@...onical.com>
Cc:     Nick Kossifidis <mick@....forth.gr>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: Don't use va_pa_offset on kdump

Στις 2021-10-06 14:13, Alexandre Ghiti έγραψε:
>> +
>> +       /* This will trigger a jump to CSR_STVEC anyway */
>>         jalr    zero, a2, 0
> 
> The last jump to a2 can be removed since the fault will be triggered
> before even reaching this instruction.
> 

Just switching SATP to zero doesn't generate a trap unless mstatus.TVM 
is set (for visualization purposes). The hart will try and execute the 
next instruction but it's not clear in the spec what happens in case the 
code is cached, I don't want to rely solely on STVEC. I prefer having 
this instruction there, note that some earlier QEMU versions also had 
this behavior (the original kdump patch didn't set STVEC and it worked 
fine after setting SATP to zero).

> 
> This patch fixes a regression introduced when moving the kernel to the
> end of the address space, so we should add:
> Fixes: 2bfc6cd81bd1 ("riscv: Move kernel mapping outside of linear 
> mapping")
> 
> And it should be backported to 5.13 and 5.14. It seems that the
> following tags should be enough:
> 
> Cc: <stable@...r.kernel.org> # 5.13
> Cc: <stable@...r.kernel.org> # 5.14
> 
> And finally, you can add:
> 
> Reviewed-by: Alexandre Ghiti <alex@...ti.fr>
> 

ACK, thanks ! I'll resend the patch with the tags you mentioned.

Regards,
Nick