[PATCH 2/3] x86: Remove pda.irqcount
From: Avi Kivity
Date: Thu Dec 25 2008 - 15:59:28 EST
pda.irqcount is used to test whether we need to switch to an irqstack or not.
We can do without it, however, by testing %rsp directly: if it's already
within the irqstack range we don't need to stacks.
This makes switching the nmi handler to use the irqstack easier.
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
---
arch/x86/include/asm/pda.h | 2 +-
arch/x86/kernel/asm-offsets_64.c | 1 -
arch/x86/kernel/cpu/common.c | 1 -
arch/x86/kernel/entry_64.S | 29 +++++++++++++----------------
4 files changed, 14 insertions(+), 19 deletions(-)
diff --git a/arch/x86/include/asm/pda.h b/arch/x86/include/asm/pda.h
index 2fbfff8..2099610 100644
--- a/arch/x86/include/asm/pda.h
+++ b/arch/x86/include/asm/pda.h
@@ -14,7 +14,7 @@ struct x8664_pda {
address */
unsigned long kernelstack; /* 16 top of kernel stack for current */
unsigned long oldrsp; /* 24 user rsp for system call */
- int irqcount; /* 32 Irq nesting counter. Starts -1 */
+ int unused; /* 32 for rent */
unsigned int cpunumber; /* 36 Logical CPU number */
#ifdef CONFIG_CC_STACKPROTECTOR
unsigned long stack_canary; /* 40 stack canary value */
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index 7fcf63d..779d010 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -50,7 +50,6 @@ int main(void)
ENTRY(kernelstack);
ENTRY(oldrsp);
ENTRY(pcurrent);
- ENTRY(irqcount);
ENTRY(cpunumber);
ENTRY(irqstackptr);
ENTRY(data_offset);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8563c51..6313d03 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -877,7 +877,6 @@ void __cpuinit pda_init(int cpu)
mb();
pda->cpunumber = cpu;
- pda->irqcount = -1;
pda->kernelstack = (unsigned long)stack_thread_info() -
PDA_STACKOFFSET + THREAD_SIZE;
pda->active_mm = &init_mm;
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 8c882e1..245fecd 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -627,6 +627,15 @@ END(stub_rt_sigreturn)
vector already pushed) */
#define XCPT_FRAME _frame ORIG_RAX
+ .macro enter_irqstack scratch
+ mov %gs:pda_irqstackptr, \scratch
+ sub %rsp, \scratch
+ cmp $IRQSTACKSIZE-64, \scratch
+ jbe 1234f
+ mov %gs:pda_irqstackptr, %rsp
+1234:
+ .endm
+
/*
* Interrupt entry/exit.
*
@@ -655,14 +664,7 @@ END(stub_rt_sigreturn)
testl $3,CS(%rdi)
je 1f
SWAPGS
- /* irqcount is used to check if a CPU is already on an interrupt
- stack or not. While this is essentially redundant with preempt_count
- it is a little cheaper to use a separate counter in the PDA
- (short of moving irq_enter into assembly, which would be too
- much work) */
-1: incl %gs:pda_irqcount
- cmoveq %gs:pda_irqstackptr,%rsp
- push %rbp # backlink for old unwinder
+1: enter_irqstack %rax
/*
* We entered an interrupt context - irqs are off:
*/
@@ -677,7 +679,6 @@ ENTRY(common_interrupt)
ret_from_intr:
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF
- decl %gs:pda_irqcount
leaveq
CFI_DEF_CFA_REGISTER rsp
CFI_ADJUST_CFA_OFFSET -8
@@ -1325,14 +1326,12 @@ ENTRY(call_softirq)
CFI_REL_OFFSET rbp,0
mov %rsp,%rbp
CFI_DEF_CFA_REGISTER rbp
- incl %gs:pda_irqcount
- cmove %gs:pda_irqstackptr,%rsp
+ enter_irqstack %rax
push %rbp # backlink for old unwinder
call __do_softirq
leaveq
CFI_DEF_CFA_REGISTER rsp
CFI_ADJUST_CFA_OFFSET -8
- decl %gs:pda_irqcount
ret
CFI_ENDPROC
ENDPROC(call_softirq)
@@ -1369,15 +1368,13 @@ ENTRY(xen_do_hypervisor_callback) # do_hypervisor_callback(struct *pt_regs)
movq %rdi, %rsp # we don't return, adjust the stack frame
CFI_ENDPROC
CFI_DEFAULT_STACK
-11: incl %gs:pda_irqcount
- movq %rsp,%rbp
+11: movq %rsp,%rbp
CFI_DEF_CFA_REGISTER rbp
- cmovzq %gs:pda_irqstackptr,%rsp
+ enter_irqstack %rax
pushq %rbp # backlink for old unwinder
call xen_evtchn_do_upcall
popq %rsp
CFI_DEF_CFA_REGISTER rsp
- decl %gs:pda_irqcount
jmp error_exit
CFI_ENDPROC
END(do_hypervisor_callback)
--
1.6.0.6
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