[v3,2/3] LoongArch: Perform alternative runtime patching on vDSO

Commit Message

Xi Ruoyao Aug. 16, 2024, 11:07 a.m. UTC

To implement getrandom() in vDSO, we need to implement stack-less
ChaCha20.  ChaCha20 is designed to be SIMD-friendly, but LSX is not
guaranteed to be available on all LoongArch CPU models.  Perform
alternative runtime patching on vDSO so we'll be able to use LSX in
vDSO.

Signed-off-by: Xi Ruoyao <[e-mail]>
---
 arch/loongarch/kernel/vdso.c   | 8 +++++++-
 arch/loongarch/vdso/vdso.lds.S | 6 ++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/loongarch/kernel/vdso.c b/arch/loongarch/kernel/vdso.c
index 15b65d8e2fdc..d500436f252b 100644
--- a/arch/loongarch/kernel/vdso.c
+++ b/arch/loongarch/kernel/vdso.c
@@ -17,6 +17,7 @@ 
 #include <linux/time_namespace.h>
 #include <linux/timekeeper_internal.h>
 
+#include <asm/alternative.h>
 #include <asm/page.h>
 #include <asm/vdso.h>
 #include <vdso/helpers.h>
@@ -105,7 +106,7 @@  struct loongarch_vdso_info vdso_info = {
 
 static int __init init_vdso(void)
 {
-	unsigned long i, cpu, pfn;
+	unsigned long i, cpu, pfn, vdso;
 
 	BUG_ON(!PAGE_ALIGNED(vdso_info.vdso));
 	BUG_ON(!PAGE_ALIGNED(vdso_info.size));
@@ -117,6 +118,11 @@  static int __init init_vdso(void)
 	for (i = 0; i < vdso_info.size / PAGE_SIZE; i++)
 		vdso_info.code_mapping.pages[i] = pfn_to_page(pfn + i);
 
+	vdso = (unsigned long)vdso_info.vdso;
+
+	apply_alternatives((struct alt_instr *)(vdso + vdso_offset_alt),
+			   (struct alt_instr *)(vdso + vdso_offset_alt_end));
+
 	return 0;
 }
 subsys_initcall(init_vdso);
diff --git a/arch/loongarch/vdso/vdso.lds.S b/arch/loongarch/vdso/vdso.lds.S
index 2c965a597d9e..ac63dc080bc9 100644
--- a/arch/loongarch/vdso/vdso.lds.S
+++ b/arch/loongarch/vdso/vdso.lds.S
@@ -35,6 +35,12 @@  SECTIONS
 
 	.rodata		: { *(.rodata*) }		:text
 
+	.altinstructions : ALIGN(4) {
+		VDSO_alt = .;
+		*(.altinstructions)
+		VDSO_alt_end = .;
+	} :text
+
 	_end = .;
 	PROVIDE(end = .);