***Background: People reported that kaslr may randomly chooses some positions which are located in movable memory regions. This will break memory hotplug feature and make the memory can't be removed.
***Solutions: There should be a method to limit kaslr to choosing immovable memory regions, so there are 2 solutions: 1) Add a kernel parameter to specify the memory regions. 2) Get the information of memory hotremove, then kaslr will know the right regions. But in method 2, information about memory hot remove is in ACPI tables, which will be parsed after 'start_kernel', kaslr can't get the information. In method 1, users should know the regions address and specify in kernel parameter. In the earliest time, I tried to dig ACPI tabls to solve this problem. But I didn't splite the code in 'compressed/' and ACPI code, so the patch is hard to follow so refused by community. Somebody suggest to add a kernel parameter to specify the immovable memory so that limit kaslr in these regions. Then I make a patchset. After several versions, Ingo gave a suggestion: https://www.mail-archive.com/[email protected]/msg1634024.html Follow Ingo's suggestion, imitate the ACPI code to parse the acpi tables, so that the kaslr can get necessary memory information in ACPI tables. Since I think ACPI code is independent part, so copy the codes and functions to 'compressed/' directory, so that kaslr won't influence the initialization of ACPI. *** Issues need be discussed There are several issues I am not quite sure, please help review and give suggestions: 1) In PATCH 1, I copy the structures and functions from ACPI head file, so that ACPI head file will never been used here. I am not sure whether it's good to include ACPI head file or use the method in PATCH 1. If people think we can use ACPI head files directely, I will remove the PATCH 1. ***Test results: - I did a very simple test, and it can get the memory information in bios and efi KVM guest machine, and put it by early printk. But no more tests, so it's with RFC tag. Any comments will be welcome. Chao Fan (4): x86/boot: Add acpitb.h to help parse acpi tables x86/boot: Add acpitb.c to parse acpi tables x86/boot/KASLR: Walk srat tables to filter immovable memory x86/boot/KASLR: Limit kaslr to choosing the immovable memory arch/x86/boot/compressed/Makefile | 1 + arch/x86/boot/compressed/acpitb.c | 245 ++++++++++++++++++++++++++++++ arch/x86/boot/compressed/acpitb.h | 175 +++++++++++++++++++++ arch/x86/boot/compressed/kaslr.c | 120 +++++++++++++-- 4 files changed, 530 insertions(+), 11 deletions(-) create mode 100644 arch/x86/boot/compressed/acpitb.c create mode 100644 arch/x86/boot/compressed/acpitb.h -- 2.17.0
