x86: entry_64.S - trivial: space, comments fixup
Impact: cleanup Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -1231,22 +1231,24 @@ END(call_softirq)
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zeroentry xen_hypervisor_callback xen_do_hypervisor_callback
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/*
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# A note on the "critical region" in our callback handler.
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# We want to avoid stacking callback handlers due to events occurring
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# during handling of the last event. To do this, we keep events disabled
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# until we've done all processing. HOWEVER, we must enable events before
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# popping the stack frame (can't be done atomically) and so it would still
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# be possible to get enough handler activations to overflow the stack.
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# Although unlikely, bugs of that kind are hard to track down, so we'd
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# like to avoid the possibility.
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# So, on entry to the handler we detect whether we interrupted an
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# existing activation in its critical region -- if so, we pop the current
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# activation and restart the handler using the previous one.
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*/
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* A note on the "critical region" in our callback handler.
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* We want to avoid stacking callback handlers due to events occurring
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* during handling of the last event. To do this, we keep events disabled
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* until we've done all processing. HOWEVER, we must enable events before
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* popping the stack frame (can't be done atomically) and so it would still
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* be possible to get enough handler activations to overflow the stack.
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* Although unlikely, bugs of that kind are hard to track down, so we'd
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* like to avoid the possibility.
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* So, on entry to the handler we detect whether we interrupted an
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* existing activation in its critical region -- if so, we pop the current
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* activation and restart the handler using the previous one.
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*/
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ENTRY(xen_do_hypervisor_callback) # do_hypervisor_callback(struct *pt_regs)
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CFI_STARTPROC
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/* Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
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see the correct pointer to the pt_regs */
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/*
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* Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
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* see the correct pointer to the pt_regs
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*/
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movq %rdi, %rsp # we don't return, adjust the stack frame
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CFI_ENDPROC
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DEFAULT_FRAME
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@ -1264,18 +1266,18 @@ ENTRY(xen_do_hypervisor_callback) # do_hypervisor_callback(struct *pt_regs)
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END(do_hypervisor_callback)
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/*
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# Hypervisor uses this for application faults while it executes.
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# We get here for two reasons:
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# 1. Fault while reloading DS, ES, FS or GS
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# 2. Fault while executing IRET
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# Category 1 we do not need to fix up as Xen has already reloaded all segment
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# registers that could be reloaded and zeroed the others.
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# Category 2 we fix up by killing the current process. We cannot use the
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# normal Linux return path in this case because if we use the IRET hypercall
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# to pop the stack frame we end up in an infinite loop of failsafe callbacks.
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# We distinguish between categories by comparing each saved segment register
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# with its current contents: any discrepancy means we in category 1.
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*/
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* Hypervisor uses this for application faults while it executes.
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* We get here for two reasons:
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* 1. Fault while reloading DS, ES, FS or GS
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* 2. Fault while executing IRET
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* Category 1 we do not need to fix up as Xen has already reloaded all segment
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* registers that could be reloaded and zeroed the others.
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* Category 2 we fix up by killing the current process. We cannot use the
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* normal Linux return path in this case because if we use the IRET hypercall
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* to pop the stack frame we end up in an infinite loop of failsafe callbacks.
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* We distinguish between categories by comparing each saved segment register
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* with its current contents: any discrepancy means we in category 1.
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*/
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ENTRY(xen_failsafe_callback)
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INTR_FRAME 1 (6*8)
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/*CFI_REL_OFFSET gs,GS*/
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