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Re: Recent patches break ACPI tables

From: luca
Subject: Re: Recent patches break ACPI tables
Date: Mon, 19 Jun 2023 19:43:05 +0200


Il 18/06/23 22:52, Samuel Thibault ha scritto:

Damien Zammit, le dim. 18 juin 2023 00:48:15 +0000, a ecrit:
Almu and I discovered that the following commit breaks --enable-apic 
--enable-ncpus= >1 --disable-linux-groups
* d972c01c pmap: only map lower BIOS memory 1:1 when using Linux drivers

I believe the ACPI tables need temporary low memory mapping to access them.

Luca, what do you think?

Can we perhaps fix the ACPI code to use phystokv to translate from
physical addresses to virtual addresses?

yes that's probably the best way to fix the code.

By the way, how, is it exactly crashing? It might not be related to ACPI/APIC code, I tried a simple program on a 32-bit kernel with --enable-apic but without --enable-ncpus and it seems to work. If I use --enable-ncpus=2 it seems to fail quite early, even without -smp=2 in qemu. At the moment I'm not able to set a breakpoint even to the C entry point, I'm not sure why, I think I did it in the past.

Maybe there is some other part, SMP_specific, that assumes the lower memory is mapped 1:1? I remember there was some bootstrap code to start the secondary cpus, but I don't remember the details.


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