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Subject[RFC PATCH 11/35] Add support for Xen to entry.S.
- change cli/sti
- change test for user mode return to work for kernel mode in ring1
- check hypervisor saved event mask on return from exception
- add entry points for the hypervisor upcall handlers
- avoid math emulation check when running on Xen
- add nmi handler for running on Xen

Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
arch/i386/kernel/entry.S | 228 +++++++++++++++++++++++++++++++++++++++++++----
1 files changed, 211 insertions(+), 17 deletions(-)

--- xen-subarch-2.6.orig/arch/i386/kernel/entry.S
+++ xen-subarch-2.6/arch/i386/kernel/entry.S
@@ -75,8 +75,42 @@ DF_MASK = 0x00000400
NT_MASK = 0x00004000
VM_MASK = 0x00020000

+#ifndef CONFIG_XEN
+#define DISABLE_INTERRUPTS cli
+#define ENABLE_INTERRUPTS sti
+#else
+#include <xen/interface/xen.h>
+
+EVENT_MASK = 0x2E
+
+/* Pseudo-eflags. */
+NMI_MASK = 0x80000000
+
+/* Offsets into shared_info_t. */
+#define evtchn_upcall_pending /* 0 */
+#define evtchn_upcall_mask 1
+
+#define sizeof_vcpu_shift 6
+
+#ifdef CONFIG_SMP
+#define GET_VCPU_INFO movl TI_cpu(%ebp),%esi ; \
+ shl $sizeof_vcpu_shift,%esi ; \
+ addl HYPERVISOR_shared_info,%esi
+#else
+#define GET_VCPU_INFO movl HYPERVISOR_shared_info,%esi
+#endif
+
+#define __DISABLE_INTERRUPTS movb $1,evtchn_upcall_mask(%esi)
+#define __ENABLE_INTERRUPTS movb $0,evtchn_upcall_mask(%esi)
+#define DISABLE_INTERRUPTS GET_VCPU_INFO ; \
+ __DISABLE_INTERRUPTS
+#define ENABLE_INTERRUPTS GET_VCPU_INFO ; \
+ __ENABLE_INTERRUPTS
+#define __TEST_PENDING testb $0xFF,evtchn_upcall_pending(%esi)
+#endif
+
#ifdef CONFIG_PREEMPT
-#define preempt_stop cli
+#define preempt_stop DISABLE_INTERRUPTS
#else
#define preempt_stop
#define resume_kernel restore_nocheck
@@ -145,10 +179,10 @@ ret_from_intr:
GET_THREAD_INFO(%ebp)
movl EFLAGS(%esp), %eax # mix EFLAGS and CS
movb CS(%esp), %al
- testl $(VM_MASK | 3), %eax
+ testl $(VM_MASK | USER_MODE_MASK), %eax
jz resume_kernel
ENTRY(resume_userspace)
- cli # make sure we don't miss an interrupt
+ DISABLE_INTERRUPTS # make sure we don't miss an interrupt
# setting need_resched or sigpending
# between sampling and the iret
movl TI_flags(%ebp), %ecx
@@ -159,7 +193,7 @@ ENTRY(resume_userspace)

#ifdef CONFIG_PREEMPT
ENTRY(resume_kernel)
- cli
+ DISABLE_INTERRUPTS
cmpl $0,TI_preempt_count(%ebp) # non-zero preempt_count ?
jnz restore_nocheck
need_resched:
@@ -179,7 +213,7 @@ need_resched:
ENTRY(sysenter_entry)
movl TSS_sysenter_esp0(%esp),%esp
sysenter_past_esp:
- sti
+ ENABLE_INTERRUPTS
pushl $(__USER_DS)
pushl %ebp
pushfl
@@ -209,7 +243,7 @@ sysenter_past_esp:
jae syscall_badsys
call *sys_call_table(,%eax,4)
movl %eax,EAX(%esp)
- cli
+ DISABLE_INTERRUPTS
movl TI_flags(%ebp), %ecx
testw $_TIF_ALLWORK_MASK, %cx
jne syscall_exit_work
@@ -217,7 +251,7 @@ sysenter_past_esp:
movl EIP(%esp), %edx
movl OLDESP(%esp), %ecx
xorl %ebp,%ebp
- sti
+ ENABLE_INTERRUPTS
sysexit


@@ -236,7 +270,7 @@ syscall_call:
call *sys_call_table(,%eax,4)
movl %eax,EAX(%esp) # store the return value
syscall_exit:
- cli # make sure we don't miss an interrupt
+ DISABLE_INTERRUPTS # make sure we don't miss an interrupt
# setting need_resched or sigpending
# between sampling and the iret
movl TI_flags(%ebp), %ecx
@@ -244,6 +278,7 @@ syscall_exit:
jne syscall_exit_work

restore_all:
+#ifndef CONFIG_XEN
movl EFLAGS(%esp), %eax # mix EFLAGS, SS and CS
# Warning: OLDSS(%esp) contains the wrong/random values if we
# are returning to the kernel.
@@ -254,12 +289,25 @@ restore_all:
cmpl $((4 << 8) | 3), %eax
je ldt_ss # returning to user-space with LDT SS
restore_nocheck:
+#else
+restore_nocheck:
+ testl $(VM_MASK|NMI_MASK), EFLAGS(%esp)
+ jnz hypervisor_iret
+ movb EVENT_MASK(%esp), %al
+ notb %al # %al == ~saved_mask
+ GET_VCPU_INFO
+ andb evtchn_upcall_mask(%esi),%al
+ andb $1,%al # %al == mask & ~saved_mask
+ jnz restore_all_enable_events # != 0 => reenable event delivery
+#endif
RESTORE_REGS
addl $4, %esp
1: iret
.section .fixup,"ax"
iret_exc:
- sti
+#ifndef CONFIG_XEN
+ ENABLE_INTERRUPTS
+#endif
pushl $0 # no error code
pushl $do_iret_error
jmp error_code
@@ -269,6 +317,7 @@ iret_exc:
.long 1b,iret_exc
.previous

+#ifndef CONFIG_XEN
ldt_ss:
larl OLDSS(%esp), %eax
jnz restore_nocheck
@@ -281,7 +330,7 @@ ldt_ss:
* CPUs, which we can try to work around to make
* dosemu and wine happy. */
subl $8, %esp # reserve space for switch16 pointer
- cli
+ DISABLE_INTERRUPTS
movl %esp, %eax
/* Set up the 16bit stack frame with switch32 pointer on top,
* and a switch16 pointer on top of the current frame. */
@@ -293,6 +342,13 @@ ldt_ss:
.align 4
.long 1b,iret_exc
.previous
+#else
+hypervisor_iret:
+ andl $~NMI_MASK, EFLAGS(%esp)
+ RESTORE_REGS
+ addl $4, %esp
+ jmp hypercall_page + (__HYPERVISOR_iret * 32)
+#endif

# perform work that needs to be done immediately before resumption
ALIGN
@@ -301,7 +357,7 @@ work_pending:
jz work_notifysig
work_resched:
call schedule
- cli # make sure we don't miss an interrupt
+ DISABLE_INTERRUPTS # make sure we don't miss an interrupt
# setting need_resched or sigpending
# between sampling and the iret
movl TI_flags(%ebp), %ecx
@@ -353,7 +409,7 @@ syscall_trace_entry:
syscall_exit_work:
testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP), %cl
jz work_pending
- sti # could let do_syscall_trace() call
+ ENABLE_INTERRUPTS # could let do_syscall_trace() call
# schedule() instead
movl %esp, %eax
movl $1, %edx
@@ -373,6 +429,7 @@ syscall_badsys:
movl $-ENOSYS,EAX(%esp)
jmp resume_userspace

+#ifndef CONFIG_XEN
#define FIXUP_ESPFIX_STACK \
movl %esp, %eax; \
/* switch to 32bit stack using the pointer on top of 16bit stack */ \
@@ -431,6 +488,9 @@ ENTRY(name) \

/* The include is where all of the SMP etc. interrupts come from */
#include "entry_arch.h"
+#else
+#define UNWIND_ESPFIX_STACK
+#endif

ENTRY(divide_error)
pushl $0 # no error code
@@ -462,6 +522,126 @@ error_code:
call *%edi
jmp ret_from_exception

+#ifdef CONFIG_XEN
+# A note on the "critical region" in our callback handler.
+# We want to avoid stacking callback handlers due to events occurring
+# during handling of the last event. To do this, we keep events disabled
+# until we've done all processing. HOWEVER, we must enable events before
+# popping the stack frame (can't be done atomically) and so it would still
+# be possible to get enough handler activations to overflow the stack.
+# Although unlikely, bugs of that kind are hard to track down, so we'd
+# like to avoid the possibility.
+# So, on entry to the handler we detect whether we interrupted an
+# existing activation in its critical region -- if so, we pop the current
+# activation and restart the handler using the previous one.
+ENTRY(hypervisor_callback)
+ pushl %eax
+ SAVE_ALL
+ movl EIP(%esp),%eax
+ cmpl $scrit,%eax
+ jb 11f
+ cmpl $ecrit,%eax
+ jb critical_region_fixup
+11: push %esp
+ call evtchn_do_upcall
+ add $4,%esp
+ jmp ret_from_intr
+
+ ALIGN
+restore_all_enable_events:
+ __ENABLE_INTERRUPTS
+scrit: /**** START OF CRITICAL REGION ****/
+ __TEST_PENDING
+ jnz 14f # process more events if necessary...
+ RESTORE_REGS
+ addl $4, %esp
+1: iret
+.section .fixup,"ax"
+2: pushl $0
+ pushl $do_iret_error
+ jmp error_code
+.previous
+.section __ex_table,"a"
+ .align 4
+ .long 1b,2b
+.previous
+14: __DISABLE_INTERRUPTS
+ jmp 11b
+ecrit: /**** END OF CRITICAL REGION ****/
+# [How we do the fixup]. We want to merge the current stack frame with the
+# just-interrupted frame. How we do this depends on where in the critical
+# region the interrupted handler was executing, and so how many saved
+# registers are in each frame. We do this quickly using the lookup table
+# 'critical_fixup_table'. For each byte offset in the critical region, it
+# provides the number of bytes which have already been popped from the
+# interrupted stack frame.
+critical_region_fixup:
+ addl $critical_fixup_table-scrit,%eax
+ movzbl (%eax),%eax # %eax contains num bytes popped
+ cmpb $0xff,%al # 0xff => vcpu_info critical region
+ jne 15f
+ GET_THREAD_INFO(%ebp)
+ xorl %eax,%eax
+15: mov %esp,%esi
+ add %eax,%esi # %esi points at end of src region
+ mov %esp,%edi
+ add $0x34,%edi # %edi points at end of dst region
+ mov %eax,%ecx
+ shr $2,%ecx # convert words to bytes
+ je 17f # skip loop if nothing to copy
+16: subl $4,%esi # pre-decrementing copy loop
+ subl $4,%edi
+ movl (%esi),%eax
+ movl %eax,(%edi)
+ loop 16b
+17: movl %edi,%esp # final %edi is top of merged stack
+ jmp 11b
+
+critical_fixup_table:
+ .byte 0xff,0xff,0xff # testb $0xff,(%esi) = __TEST_PENDING
+ .byte 0xff,0xff # jnz 14f
+ .byte 0x00 # pop %ebx
+ .byte 0x04 # pop %ecx
+ .byte 0x08 # pop %edx
+ .byte 0x0c # pop %esi
+ .byte 0x10 # pop %edi
+ .byte 0x14 # pop %ebp
+ .byte 0x18 # pop %eax
+ .byte 0x1c # pop %ds
+ .byte 0x20 # pop %es
+ .byte 0x24,0x24,0x24 # add $4,%esp
+ .byte 0x28 # iret
+ .byte 0xff,0xff,0xff,0xff # movb $1,1(%esi)
+ .byte 0x00,0x00 # jmp 11b
+
+# Hypervisor uses this for application faults while it executes.
+ENTRY(failsafe_callback)
+1: popl %ds
+2: popl %es
+3: popl %fs
+4: popl %gs
+ subl $4,%esp
+ SAVE_ALL
+ jmp ret_from_exception
+.section .fixup,"ax"; \
+6: movl $0,(%esp); \
+ jmp 1b; \
+7: movl $0,(%esp); \
+ jmp 2b; \
+8: movl $0,(%esp); \
+ jmp 3b; \
+9: movl $0,(%esp); \
+ jmp 4b; \
+.previous; \
+.section __ex_table,"a";\
+ .align 4; \
+ .long 1b,6b; \
+ .long 2b,7b; \
+ .long 3b,8b; \
+ .long 4b,9b; \
+.previous
+#endif
+
ENTRY(coprocessor_error)
pushl $0
pushl $do_coprocessor_error
@@ -475,17 +655,19 @@ ENTRY(simd_coprocessor_error)
ENTRY(device_not_available)
pushl $-1 # mark this as an int
SAVE_ALL
+#ifndef CONFIG_XEN
movl %cr0, %eax
testl $0x4, %eax # EM (math emulation bit)
- jne device_not_available_emulate
- preempt_stop
- call math_state_restore
- jmp ret_from_exception
-device_not_available_emulate:
+ je device_available_emulate
pushl $0 # temporary storage for ORIG_EIP
call math_emulate
addl $4, %esp
jmp ret_from_exception
+device_available_emulate:
+#endif
+ preempt_stop
+ call math_state_restore
+ jmp ret_from_exception

/*
* Debug traps and NMI can happen at the one SYSENTER instruction
@@ -521,6 +703,8 @@ debug_stack_correct:
call do_debug
jmp ret_from_exception
.previous .text
+
+#ifndef CONFIG_XEN
/*
* NMI is doubly nasty. It can happen _while_ we're handling
* a debug fault, and the debug fault hasn't yet been able to
@@ -591,6 +775,16 @@ nmi_16bit_stack:
.align 4
.long 1b,iret_exc
.previous
+#else
+ENTRY(nmi)
+ pushl %eax
+ SAVE_ALL
+ xorl %edx,%edx # zero error code
+ movl %esp,%eax # pt_regs pointer
+ call do_nmi
+ orl $NMI_MASK, EFLAGS(%esp)
+ jmp restore_all
+#endif

KPROBE_ENTRY(int3)
pushl $-1 # mark this as an int
--
-
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