[PATCH 3/5] x86, paravirt: Replace GET_CR2_INTO_RCX with GET_CR2_INTO_RAX

From: H. Peter Anvin
Date: Wed Apr 18 2012 - 20:18:14 EST

From: "H. Peter Anvin" <hpa@xxxxxxxxx>

GET_CR2_INTO_RCX is asinine: it is only used in one place, the actual
paravirt call returns the value in %rax, not %rcx; and the one place
that wants it wants the result in %r9. We actually generate as a
result of this call:

call ...
movq %rax, %rcx
xorq %rax, %rax /* this value isn't even used... */
movq %rcx, %r9

At least make the macro do what the paravirt call does, which is put
the value into %rax.

Nevermind the fact that the macro clobbers all the volatile registers.

Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>
arch/x86/include/asm/paravirt.h | 6 ++----
arch/x86/kernel/head_64.S | 6 +++---
2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index aa0f913..6cbbabf 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -1023,10 +1023,8 @@ extern void default_banner(void);
call PARA_INDIRECT(pv_cpu_ops+PV_CPU_swapgs) \

-#define GET_CR2_INTO_RCX \
- call PARA_INDIRECT(pv_mmu_ops+PV_MMU_read_cr2); \
- movq %rax, %rcx; \
- xorq %rax, %rax;
+#define GET_CR2_INTO_RAX \
+ call PARA_INDIRECT(pv_mmu_ops+PV_MMU_read_cr2)

PARA_SITE(PARA_PATCH(pv_irq_ops, PV_IRQ_adjust_exception_frame), \
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index adf52e8..d1e112c 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -23,8 +23,9 @@
#include <asm/asm-offsets.h>
#include <asm/paravirt.h>
+#define GET_CR2_INTO(reg) GET_CR2_INTO_RAX ; movq %rax, reg
-#define GET_CR2_INTO_RCX movq %cr2, %rcx
+#define GET_CR2_INTO(reg) movq %cr2, reg

/* we are not able to switch in one step to the final KERNEL ADDRESS SPACE
@@ -286,8 +287,7 @@ ENTRY(early_idt_handler)
cmpl $2,early_recursion_flag(%rip)
jz 1f
incl early_recursion_flag(%rip)
- movq %rcx,%r9
+ GET_CR2_INTO(%r9)
xorl %r8d,%r8d # zero for error code
movl %esi,%ecx # get vector number
# Test %ecx against mask of vectors that push error code.

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