Hi Dave, Thanks for bringing this up, > -----Original Message----- > From: Dave Young <dyoung@xxxxxxxxxx> > Sent: Friday, January 10, 2025 2:30 PM > To: Chen, Yu C <yu.c.chen@xxxxxxxxx> > Cc: x86@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; kexec@xxxxxxxxxxxxxxxxxxx; > Ingo Molnar <mingo@xxxxxxxxxx>; Borislav Petkov <bp@xxxxxxxxx> > Subject: Re: [PATCH] x86/e820: update code comment about > e820_table_kexec > > > BTW, the conversation below drived me to read the e820 code: > > https://lore.kernel.org/all/CAMj1kXG1hbiafKRyC5qM1Vj5X7x- > dmLndqqo2AYnH > > MRxDz-80w@xxxxxxxxxxxxxx/T/#u > > > > It could be better to clean up the e820 tables, anyway the comment fix > > in this patch itself is good for now. > > > > Basically e820_table_firmware is used by kexec-tools kexec_load > > implementation, e820_table_kexec is used by kexec_file_load code to > > pass to the 2nd kernel in boot params. > > > > The e820_table_firmware is said to not be modified by the kernel in > > the code comment, but this is not true, at least the sev code updates > > the table. The hibernate code generates crc32 checksum and verifies > > it, but since AFAIK e820 table update only happens in boot phase, it > > will be stable on runtime. So we can just use e820_table_firmware for > > kexec use and drop the e820_table_kexec. With the change the > > kexec_file_load and kexec_load see the same memory ranges. > > > > Otherwise I thought we can use just one e820 table, dropping > > e820_table_firmware and e820_table_kexec, but then there will be > > fragments and memory waste due to the setup_data ranges are reserved > > and updated in e820_table, so the e820_table_firmware being still be > > used for kexec makes sense. > > > > Anyway I need to think more about it, please let me know if you have > > any concerns. > > Reread the old commit 12df216c61c89e31e27e74146115a9728880ca6f > x86/boot/e820: Introduce the bootloader provided e820_table_firmware[] > table > > It seems the e820_table_firmware was changed to be exported in sysfs > instead of e820_table_kexec, but I suspect this is wrong. > kexec-tools (kexec_load) use the exported sysfs memmap info, but > e820_table_firmware was created by above commit to be used by hibernation > and the table should not be changed, the fact is there are changes happen > from time to time. > This is not expected from the original introducing of e820_table_firmware, it should not be changed by OS. I suppose the changes to e820_table_firmware are because of the kexec requirements for /sys/firmware/memmap? Another question is that, why does kexec_load() get the memory layout from /sys/firmware/memmap, but kexec_file_load() relies on the in-kernel e820_table_kexec? > Question is does hibernation use the sysfs entries from its userspace tools? Hibernation does not use this sysfs entries in userspace(or uswsusp )as far as I know. > If yes, then we should have both kexec table and firmware table exported > because they are for different purposes and one may change, another not. > > If hibernation only uses the table within the kernel then it makes no sense to > export it to sysfs, we should only export the kexec table for kexec-tools use. > In this way both kexec_load (userspace) and kexec_file_load (kernel load) can > use same e820 table, it will reduce the bugs and be easier to maintain. I'm OK with not exposing e820_table_firmware to /sys/firmware/memmap, if kexec is the only user of /sys/firmware/memmap. Thanks, Chenyu
