From: Nikolay Borisov Date: Wed, 29 May 2024 15:28:50 +0000 (+0300) Subject: x86/kexec: Remove spurious unconditional JMP from from identity_mapped() X-Git-Tag: io_uring-6.11-20240722~107^2~19 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=54183d103d38e5efefce8500ec41dfbfaba9c19d;p=linux-block.git x86/kexec: Remove spurious unconditional JMP from from identity_mapped() This seemingly straightforward JMP was introduced in the initial version of the the 64bit kexec code without any explanation. It turns out (check accompanying Link) it's likely a copy/paste artefact from 32-bit code, where such a JMP could be used as a serializing instruction for the 486's prefetch queue. On x86_64 that's not needed because there's already a preceding write to cr4 which itself is a serializing operation. [ bp: Typos. Let's try this and see what cries out. If it does, reverting it is trivial. ] Signed-off-by: Nikolay Borisov Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/all/55bc0649-c017-49ab-905d-212f140a403f@citrix.com/ --- diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S index 56cab1bb25f5..54e620021c7e 100644 --- a/arch/x86/kernel/relocate_kernel_64.S +++ b/arch/x86/kernel/relocate_kernel_64.S @@ -153,9 +153,6 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) 1: movq %rax, %cr4 - jmp 1f -1: - /* Flush the TLB (needed?) */ movq %r9, %cr3