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-rw-r--r--arch/powerpc/kernel/exceptions-64s.S28
1 files changed, 14 insertions, 14 deletions
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index e6d8354d79ef..9029afd1fa2a 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -824,7 +824,7 @@ EXC_COMMON(trap_0b_common, 0xb00, unknown_exception)
* r3 volatile parameter and return value for status
* r4-r10 volatile input and output value
* r11 volatile hypercall number and output value
- * r12 volatile
+ * r12 volatile input and output value
* r13-r31 nonvolatile
* LR nonvolatile
* CTR volatile
@@ -834,25 +834,26 @@ EXC_COMMON(trap_0b_common, 0xb00, unknown_exception)
* Other registers nonvolatile
*
* The intersection of volatile registers that don't contain possible
- * inputs is: r12, cr0, xer, ctr. We may use these as scratch regs
- * upon entry without saving.
+ * inputs is: cr0, xer, ctr. We may use these as scratch regs upon entry
+ * without saving, though xer is not a good idea to use, as hardware may
+ * interpret some bits so it may be costly to change them.
*/
#ifdef CONFIG_KVM_BOOK3S_64_HANDLER
/*
* There is a little bit of juggling to get syscall and hcall
- * working well. Save r10 in ctr to be restored in case it is a
- * hcall.
+ * working well. Save r13 in ctr to avoid using SPRG scratch
+ * register.
*
* Userspace syscalls have already saved the PPR, hcalls must save
* it before setting HMT_MEDIUM.
*/
#define SYSCALL_KVMTEST \
- mr r12,r13; \
+ mtctr r13; \
GET_PACA(r13); \
- mtctr r10; \
+ std r10,PACA_EXGEN+EX_R10(r13); \
KVMTEST_PR(0xc00); /* uses r10, branch to do_kvm_0xc00_system_call */ \
HMT_MEDIUM; \
- mr r9,r12; \
+ mfctr r9;
#else
#define SYSCALL_KVMTEST \
@@ -935,8 +936,8 @@ EXC_VIRT_END(system_call, 0x4c00, 0x100)
* This is a hcall, so register convention is as above, with these
* differences:
* r13 = PACA
- * r12 = orig r13
- * ctr = orig r10
+ * ctr = orig r13
+ * orig r10 saved in PACA
*/
TRAMP_KVM_BEGIN(do_kvm_0xc00)
/*
@@ -944,14 +945,13 @@ TRAMP_KVM_BEGIN(do_kvm_0xc00)
* HMT_MEDIUM. That allows the KVM code to save that value into the
* guest state (it is the guest's PPR value).
*/
- OPT_GET_SPR(r0, SPRN_PPR, CPU_FTR_HAS_PPR)
+ OPT_GET_SPR(r10, SPRN_PPR, CPU_FTR_HAS_PPR)
HMT_MEDIUM
- OPT_SAVE_REG_TO_PACA(PACA_EXGEN+EX_PPR, r0, CPU_FTR_HAS_PPR)
+ OPT_SAVE_REG_TO_PACA(PACA_EXGEN+EX_PPR, r10, CPU_FTR_HAS_PPR)
mfctr r10
- SET_SCRATCH0(r12)
+ SET_SCRATCH0(r10)
std r9,PACA_EXGEN+EX_R9(r13)
mfcr r9
- std r10,PACA_EXGEN+EX_R10(r13)
KVM_HANDLER(PACA_EXGEN, EXC_STD, 0xc00)
#endif