On 06/06/2024 12:01, Steven Rostedt wrote: > Reserve unspecified location of physical memory from kernel command line > [...] > Solution: > > The solution I have come up with is to introduce a new "reserve_mem=" kernel > command line. This parameter takes the following format: > > reserve_mem=nn:align:label > > Where nn is the size of memory to reserve, the align is the alignment of > that memory, and label is the way for other sub-systems to find that memory. > This way the kernel command line could have: > > reserve_mem=12M:4096:oops ramoops.mem_name=oops > > At boot up, the kernel will search for 12 megabytes in usable memory regions > with an alignment of 4096. It will start at the highest regions and work its > way down (for those old devices that want access to lower address DMA). When > it finds a region, it will save it off in a small table and mark it with the > "oops" label. Then the pstore ramoops sub-system could ask for that memory > and location, and it will map itself there. > > This prototype allows for 8 different mappings (which may be overkill, 4 is > probably plenty) with 16 byte size to store the label. > > I have tested this and it works for us to solve the above problem. We can > update the kernel and command line and increase the size of pstore without > needing to update the firmware, or knowing every memory layout of each > board. I only tested this locally, it has not been tested in the field. > Hi Steve, first of all, thanks for this work! This is much appreciated. The kdumpst tooling (Arch Linux) makes use of pstore when available, and the recommendation so far was to reserve memory somehow, like "mem=" or use kdump instead, if no free RAM area was available. With your solution, things get way more "elegant". Also, I think we all know pstore is not 100% reliable, specially the RAM backend due to already mentioned reasons (like FW memory retraining, ECC memory, etc), but it's great we have a mechanism to **try it**. If it works, awesome - for statistical analysis, this is very useful; pstore has been used with success in the Steam Deck, for example. With all that said, I've tested your patches on top of 6.10-rc2 in 2 qemu VMs (one running legacy BIOS - seabios - and the other UEFI - using ovmf) and on Steam Deck, and it's working flawlessly. I've tested only using ramoops as module. Some code review in the patches themselves (like a missing EXPORT_SYMBOL_GPL), but all in all, that's a great addition! Feel free to add my: Tested-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> Thanks, Guilherme
