+++ /dev/null
-/*
- Asm versions of Xen pv-ops, suitable for either direct use or inlining.
- The inline versions are the same as the direct-use versions, with the
- pre- and post-amble chopped off.
-
- This code is encoded for size rather than absolute efficiency,
- with a view to being able to inline as much as possible.
-
- We only bother with direct forms (ie, vcpu in pda) of the operations
- here; the indirect forms are better handled in C, since they're
- generally too large to inline anyway.
- */
-
-#include <linux/linkage.h>
-
-#include <asm/asm-offsets.h>
-#include <asm/thread_info.h>
-#include <asm/percpu.h>
-#include <asm/processor-flags.h>
-#include <asm/segment.h>
-
-#include <xen/interface/xen.h>
-
-#define RELOC(x, v) .globl x##_reloc; x##_reloc=v
-#define ENDPATCH(x) .globl x##_end; x##_end=.
-
-/* Pseudo-flag used for virtual NMI, which we don't implement yet */
-#define XEN_EFLAGS_NMI 0x80000000
-
-/*
- Enable events. This clears the event mask and tests the pending
- event status with one and operation. If there are pending
- events, then enter the hypervisor to get them handled.
- */
-ENTRY(xen_irq_enable_direct)
- /* Unmask events */
- movb $0, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
-
- /* Preempt here doesn't matter because that will deal with
- any pending interrupts. The pending check may end up being
- run on the wrong CPU, but that doesn't hurt. */
-
- /* Test for pending */
- testb $0xff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending
- jz 1f
-
-2: call check_events
-1:
-ENDPATCH(xen_irq_enable_direct)
- ret
- ENDPROC(xen_irq_enable_direct)
- RELOC(xen_irq_enable_direct, 2b+1)
-
-
-/*
- Disabling events is simply a matter of making the event mask
- non-zero.
- */
-ENTRY(xen_irq_disable_direct)
- movb $1, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
-ENDPATCH(xen_irq_disable_direct)
- ret
- ENDPROC(xen_irq_disable_direct)
- RELOC(xen_irq_disable_direct, 0)
-
-/*
- (xen_)save_fl is used to get the current interrupt enable status.
- Callers expect the status to be in X86_EFLAGS_IF, and other bits
- may be set in the return value. We take advantage of this by
- making sure that X86_EFLAGS_IF has the right value (and other bits
- in that byte are 0), but other bits in the return value are
- undefined. We need to toggle the state of the bit, because
- Xen and x86 use opposite senses (mask vs enable).
- */
-ENTRY(xen_save_fl_direct)
- testb $0xff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
- setz %ah
- addb %ah,%ah
-ENDPATCH(xen_save_fl_direct)
- ret
- ENDPROC(xen_save_fl_direct)
- RELOC(xen_save_fl_direct, 0)
-
-
-/*
- In principle the caller should be passing us a value return
- from xen_save_fl_direct, but for robustness sake we test only
- the X86_EFLAGS_IF flag rather than the whole byte. After
- setting the interrupt mask state, it checks for unmasked
- pending events and enters the hypervisor to get them delivered
- if so.
- */
-ENTRY(xen_restore_fl_direct)
- testb $X86_EFLAGS_IF>>8, %ah
- setz PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
- /* Preempt here doesn't matter because that will deal with
- any pending interrupts. The pending check may end up being
- run on the wrong CPU, but that doesn't hurt. */
-
- /* check for unmasked and pending */
- cmpw $0x0001, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending
- jz 1f
-2: call check_events
-1:
-ENDPATCH(xen_restore_fl_direct)
- ret
- ENDPROC(xen_restore_fl_direct)
- RELOC(xen_restore_fl_direct, 2b+1)
-
-/*
- We can't use sysexit directly, because we're not running in ring0.
- But we can easily fake it up using iret. Assuming xen_sysexit
- is jumped to with a standard stack frame, we can just strip it
- back to a standard iret frame and use iret.
- */
-ENTRY(xen_sysexit)
- movl PT_EAX(%esp), %eax /* Shouldn't be necessary? */
- orl $X86_EFLAGS_IF, PT_EFLAGS(%esp)
- lea PT_EIP(%esp), %esp
-
- jmp xen_iret
-ENDPROC(xen_sysexit)
-
-/*
- This is run where a normal iret would be run, with the same stack setup:
- 8: eflags
- 4: cs
- esp-> 0: eip
-
- This attempts to make sure that any pending events are dealt
- with on return to usermode, but there is a small window in
- which an event can happen just before entering usermode. If
- the nested interrupt ends up setting one of the TIF_WORK_MASK
- pending work flags, they will not be tested again before
- returning to usermode. This means that a process can end up
- with pending work, which will be unprocessed until the process
- enters and leaves the kernel again, which could be an
- unbounded amount of time. This means that a pending signal or
- reschedule event could be indefinitely delayed.
-
- The fix is to notice a nested interrupt in the critical
- window, and if one occurs, then fold the nested interrupt into
- the current interrupt stack frame, and re-process it
- iteratively rather than recursively. This means that it will
- exit via the normal path, and all pending work will be dealt
- with appropriately.
-
- Because the nested interrupt handler needs to deal with the
- current stack state in whatever form its in, we keep things
- simple by only using a single register which is pushed/popped
- on the stack.
- */
-ENTRY(xen_iret)
- /* test eflags for special cases */
- testl $(X86_EFLAGS_VM | XEN_EFLAGS_NMI), 8(%esp)
- jnz hyper_iret
-
- push %eax
- ESP_OFFSET=4 # bytes pushed onto stack
-
- /* Store vcpu_info pointer for easy access. Do it this
- way to avoid having to reload %fs */
-#ifdef CONFIG_SMP
- GET_THREAD_INFO(%eax)
- movl TI_cpu(%eax),%eax
- movl __per_cpu_offset(,%eax,4),%eax
- mov per_cpu__xen_vcpu(%eax),%eax
-#else
- movl per_cpu__xen_vcpu, %eax
-#endif
-
- /* check IF state we're restoring */
- testb $X86_EFLAGS_IF>>8, 8+1+ESP_OFFSET(%esp)
-
- /* Maybe enable events. Once this happens we could get a
- recursive event, so the critical region starts immediately
- afterwards. However, if that happens we don't end up
- resuming the code, so we don't have to be worried about
- being preempted to another CPU. */
- setz XEN_vcpu_info_mask(%eax)
-xen_iret_start_crit:
-
- /* check for unmasked and pending */
- cmpw $0x0001, XEN_vcpu_info_pending(%eax)
-
- /* If there's something pending, mask events again so we
- can jump back into xen_hypervisor_callback */
- sete XEN_vcpu_info_mask(%eax)
-
- popl %eax
-
- /* From this point on the registers are restored and the stack
- updated, so we don't need to worry about it if we're preempted */
-iret_restore_end:
-
- /* Jump to hypervisor_callback after fixing up the stack.
- Events are masked, so jumping out of the critical
- region is OK. */
- je xen_hypervisor_callback
-
-1: iret
-xen_iret_end_crit:
-.section __ex_table,"a"
- .align 4
- .long 1b,iret_exc
-.previous
-
-hyper_iret:
- /* put this out of line since its very rarely used */
- jmp hypercall_page + __HYPERVISOR_iret * 32
-
- .globl xen_iret_start_crit, xen_iret_end_crit
-
-/*
- This is called by xen_hypervisor_callback in entry.S when it sees
- that the EIP at the time of interrupt was between xen_iret_start_crit
- and xen_iret_end_crit. We're passed the EIP in %eax so we can do
- a more refined determination of what to do.
-
- The stack format at this point is:
- ----------------
- ss : (ss/esp may be present if we came from usermode)
- esp :
- eflags } outer exception info
- cs }
- eip }
- ---------------- <- edi (copy dest)
- eax : outer eax if it hasn't been restored
- ----------------
- eflags } nested exception info
- cs } (no ss/esp because we're nested
- eip } from the same ring)
- orig_eax }<- esi (copy src)
- - - - - - - - -
- fs }
- es }
- ds } SAVE_ALL state
- eax }
- : :
- ebx }<- esp
- ----------------
-
- In order to deliver the nested exception properly, we need to shift
- everything from the return addr up to the error code so it
- sits just under the outer exception info. This means that when we
- handle the exception, we do it in the context of the outer exception
- rather than starting a new one.
-
- The only caveat is that if the outer eax hasn't been
- restored yet (ie, it's still on stack), we need to insert
- its value into the SAVE_ALL state before going on, since
- it's usermode state which we eventually need to restore.
- */
-ENTRY(xen_iret_crit_fixup)
- /*
- Paranoia: Make sure we're really coming from kernel space.
- One could imagine a case where userspace jumps into the
- critical range address, but just before the CPU delivers a GP,
- it decides to deliver an interrupt instead. Unlikely?
- Definitely. Easy to avoid? Yes. The Intel documents
- explicitly say that the reported EIP for a bad jump is the
- jump instruction itself, not the destination, but some virtual
- environments get this wrong.
- */
- movl PT_CS(%esp), %ecx
- andl $SEGMENT_RPL_MASK, %ecx
- cmpl $USER_RPL, %ecx
- je 2f
-
- lea PT_ORIG_EAX(%esp), %esi
- lea PT_EFLAGS(%esp), %edi
-
- /* If eip is before iret_restore_end then stack
- hasn't been restored yet. */
- cmp $iret_restore_end, %eax
- jae 1f
-
- movl 0+4(%edi),%eax /* copy EAX (just above top of frame) */
- movl %eax, PT_EAX(%esp)
-
- lea ESP_OFFSET(%edi),%edi /* move dest up over saved regs */
-
- /* set up the copy */
-1: std
- mov $PT_EIP / 4, %ecx /* saved regs up to orig_eax */
- rep movsl
- cld
-
- lea 4(%edi),%esp /* point esp to new frame */
-2: jmp xen_do_upcall
-
-
-/*
- Force an event check by making a hypercall,
- but preserve regs before making the call.
- */
-check_events:
- push %eax
- push %ecx
- push %edx
- call force_evtchn_callback
- pop %edx
- pop %ecx
- pop %eax
- ret
git.openpandora.org / pandora-kernel.git / blobdiff