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Message-ID: <8b52b0b8513a34b2a02fb4abb05c6700c2821475.1724573384.git.kai.huang@intel.com> Date: Sun, 25 Aug 2024 20:18:06 +1200 From: Kai Huang <kai.huang@...el.com> To: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com, hpa@...or.com, peterz@...radead.org Cc: kirill.shutemov@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org, nik.borisov@...e.com Subject: [PATCH v2 2/2] x86/kexec: Add comments around swap_pages() assembly to improve readability The current assembly around swap_pages() in the relocate_kernel() takes some time to follow because the use of registers can be easily lost when the line of assembly goes long. Add a couple of comments to clarify the code around swap_pages() to improve readability. Signed-off-by: Kai Huang <kai.huang@...el.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> --- arch/x86/kernel/relocate_kernel_64.S | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S index f7a3ca3dee53..e9e88c342f75 100644 --- a/arch/x86/kernel/relocate_kernel_64.S +++ b/arch/x86/kernel/relocate_kernel_64.S @@ -170,6 +170,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) wbinvd .Lsme_off: + /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */ movq %rcx, %r11 call swap_pages @@ -289,18 +290,21 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages) movq %rcx, %rsi /* For ever source page do a copy */ andq $0xfffffffffffff000, %rsi - movq %rdi, %rdx - movq %rsi, %rax + movq %rdi, %rdx /* Save destination page to %rdx */ + movq %rsi, %rax /* Save source page to %rax */ + /* copy source page to swap page */ movq %r10, %rdi movl $512, %ecx rep ; movsq + /* copy destination page to source page */ movq %rax, %rdi movq %rdx, %rsi movl $512, %ecx rep ; movsq + /* copy swap page to destination page */ movq %rdx, %rdi movq %r10, %rsi movl $512, %ecx -- 2.46.0
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