Hi John, On 10/23/23 at 02:54pm, John Sperbeck wrote: > On Sun, Oct 22, 2023 at 7:42 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote: ...... > > >--- > > > arch/x86/kernel/kexec-bzimage64.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > >diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c > > >index a61c12c01270..d6bf6c13dab1 100644 > > >--- a/arch/x86/kernel/kexec-bzimage64.c > > >+++ b/arch/x86/kernel/kexec-bzimage64.c > > >@@ -36,7 +36,7 @@ > > > */ > > > #define MIN_PURGATORY_ADDR 0x3000 > > > #define MIN_BOOTPARAM_ADDR 0x3000 > > >-#define MIN_KERNEL_LOAD_ADDR 0x100000 > > >+#define MIN_KERNEL_LOAD_ADDR 0x1000000 > > > #define MIN_INITRD_LOAD_ADDR 0x1000000 > > > > > > /* > > > > This doesn't make any sense to me. There is already a high water mark for his much memory the kernel needs until an initrd or setup_data item can appear. This is just a hack, please fix it properly. > > The startup_64() code in head_64.S changes behavior based on whether > it's running below or above LOAD_PHYSICAL_ADDR: > > #ifdef CONFIG_RELOCATABLE > leaq startup_32(%rip) /* - $startup_32 */, %rbp > movl BP_kernel_alignment(%rsi), %eax > decl %eax > addq %rax, %rbp > notq %rax > andq %rax, %rbp > cmpq $LOAD_PHYSICAL_ADDR, %rbp > jae 1f > #endif > movq $LOAD_PHYSICAL_ADDR, %rbp > 1: > > In my example, we were running from address 0x00400000. The %rbp > register will start with 0x00400000, but will be changed to 0x01000000 > after the check against LOAD_PHYSICAL_ADDR fails. > > The 0x01000000 value in %rbp is passed to extract_kernel as the > 'output' argument. Unless choose_random_location() decides > differently, this will be where the kernel is decompressed to. The > size of the kernel is large enough in my example that the > decompression overruns the initrd. > > If the startup_64() code didn't have the LOAD_PHYSICAL_ADDR check and > used %rpb as is, then there would be no issue. The decompression > would have been to 0x00400000 and would have completed before reaching > the initrd memory. > > That is, the kexec code is being careful to ensure that the kernel and > initrd memory doesn't overlap, but isn't paying attention to what > happens if the kernel memory is below LOAD_PHYSICAL_ADDR (the kernel > address is effectively changed to a different location). My proposed > change makes it aware, and avoids such addresses. Wondering why kexec-ed kernel is located under 0x1000000. The loading code will search physical memory regions bottom up for an available one. Usually, kexec kernel will be loaded above 16M. I have posted a patchset to load kernel at top of system RAM for kexec_file load just as kexec_load has been doing. Do you think it's helpful? [PATCH 0/2] kexec_file: Load kernel at top of system RAM if required https://lore.kernel.org/all/20231114091658.228030-1-bhe@xxxxxxxxxx/T/#u Thanks Baoquan _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
