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fb58e30091
If CONFIG_PREEMPT is enabled then xen_enable_irq() (and xen_restore_fl()) could be preempted and rescheduled on a different VCPU in between the clear of the mask and the check for pending events. This may result in events being lost as the upcall will check for pending events on the wrong VCPU. Fix this by disabling preemption around the unmask and check for events. Signed-off-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
133 lines
3.1 KiB
C
133 lines
3.1 KiB
C
#include <linux/hardirq.h>
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#include <asm/x86_init.h>
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#include <xen/interface/xen.h>
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#include <xen/interface/sched.h>
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#include <xen/interface/vcpu.h>
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#include <xen/events.h>
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#include <asm/xen/hypercall.h>
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#include <asm/xen/hypervisor.h>
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#include "xen-ops.h"
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/*
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* Force a proper event-channel callback from Xen after clearing the
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* callback mask. We do this in a very simple manner, by making a call
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* down into Xen. The pending flag will be checked by Xen on return.
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*/
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void xen_force_evtchn_callback(void)
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{
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(void)HYPERVISOR_xen_version(0, NULL);
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}
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static unsigned long xen_save_fl(void)
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{
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struct vcpu_info *vcpu;
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unsigned long flags;
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vcpu = this_cpu_read(xen_vcpu);
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/* flag has opposite sense of mask */
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flags = !vcpu->evtchn_upcall_mask;
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/* convert to IF type flag
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-0 -> 0x00000000
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-1 -> 0xffffffff
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*/
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return (-flags) & X86_EFLAGS_IF;
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}
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PV_CALLEE_SAVE_REGS_THUNK(xen_save_fl);
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static void xen_restore_fl(unsigned long flags)
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{
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struct vcpu_info *vcpu;
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/* convert from IF type flag */
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flags = !(flags & X86_EFLAGS_IF);
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/* See xen_irq_enable() for why preemption must be disabled. */
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preempt_disable();
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vcpu = this_cpu_read(xen_vcpu);
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vcpu->evtchn_upcall_mask = flags;
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if (flags == 0) {
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barrier(); /* unmask then check (avoid races) */
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if (unlikely(vcpu->evtchn_upcall_pending))
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xen_force_evtchn_callback();
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preempt_enable();
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} else
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preempt_enable_no_resched();
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}
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PV_CALLEE_SAVE_REGS_THUNK(xen_restore_fl);
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static void xen_irq_disable(void)
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{
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/* There's a one instruction preempt window here. We need to
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make sure we're don't switch CPUs between getting the vcpu
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pointer and updating the mask. */
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preempt_disable();
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this_cpu_read(xen_vcpu)->evtchn_upcall_mask = 1;
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preempt_enable_no_resched();
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}
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PV_CALLEE_SAVE_REGS_THUNK(xen_irq_disable);
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static void xen_irq_enable(void)
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{
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struct vcpu_info *vcpu;
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/*
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* We may be preempted as soon as vcpu->evtchn_upcall_mask is
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* cleared, so disable preemption to ensure we check for
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* events on the VCPU we are still running on.
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*/
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preempt_disable();
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vcpu = this_cpu_read(xen_vcpu);
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vcpu->evtchn_upcall_mask = 0;
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/* Doesn't matter if we get preempted here, because any
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pending event will get dealt with anyway. */
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barrier(); /* unmask then check (avoid races) */
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if (unlikely(vcpu->evtchn_upcall_pending))
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xen_force_evtchn_callback();
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preempt_enable();
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}
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PV_CALLEE_SAVE_REGS_THUNK(xen_irq_enable);
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static void xen_safe_halt(void)
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{
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/* Blocking includes an implicit local_irq_enable(). */
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if (HYPERVISOR_sched_op(SCHEDOP_block, NULL) != 0)
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BUG();
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}
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static void xen_halt(void)
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{
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if (irqs_disabled())
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HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
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else
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xen_safe_halt();
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}
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static const struct pv_irq_ops xen_irq_ops __initconst = {
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.save_fl = PV_CALLEE_SAVE(xen_save_fl),
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.restore_fl = PV_CALLEE_SAVE(xen_restore_fl),
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.irq_disable = PV_CALLEE_SAVE(xen_irq_disable),
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.irq_enable = PV_CALLEE_SAVE(xen_irq_enable),
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.safe_halt = xen_safe_halt,
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.halt = xen_halt,
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#ifdef CONFIG_X86_64
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.adjust_exception_frame = xen_adjust_exception_frame,
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#endif
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};
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void __init xen_init_irq_ops(void)
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{
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pv_irq_ops = xen_irq_ops;
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x86_init.irqs.intr_init = xen_init_IRQ;
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}
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