Messages in this thread | | | Date | Sat, 23 Oct 2021 13:14:11 -0700 (PDT) | Subject | Re: [PATCH] riscv: Don't use va_pa_offset on kdump | From | Palmer Dabbelt <> |
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On Sat, 09 Oct 2021 06:18:48 PDT (-0700), mick@ics.forth.gr wrote: > 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).
IIRC this came down to some very specific wording in the spec. Something along the lines of the 0 in SATP meaning "no translation", SFENCE.VMA ordering translations, and the general "if the spec doesn't mention it then it has to work" logic. I thought I opened a spec issue about this for clarification, but I can't find it.
That said, I'm perfectly fine taking the safe approach here as it's not like the performance matters here. Warrants a comment, though.
> >> >> 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@vger.kernel.org> # 5.13 >> Cc: <stable@vger.kernel.org> # 5.14 >> >> And finally, you can add: >> >> Reviewed-by: Alexandre Ghiti <alex@ghiti.fr> >> > > ACK, thanks ! I'll resend the patch with the tags you mentioned.
I don't have a v2 in my inbox, did I miss something? Also, if it's just the tags then it's generally not necessary to re-send something. The comment does, though.
LMK if you want me to deal with this, or if there's going to be a v2.
Thanks!
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