From d669811e11f325378294f31f138075af50b7258f Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Tue, 11 Feb 2014 15:41:03 +0000 Subject: [PATCH] x86/xen: allow privcmd hypercalls to be preempted Hypercalls submitted by user space tools via the privcmd driver can take a long time (potentially many 10s of seconds) if the hypercall has many sub-operations. A fully preemptible kernel may deschedule such as task in any upcall called from a hypercall continuation. However, in a kernel with voluntary or no preemption, hypercall continuations in Xen allow event handlers to be run but the task issuing the hypercall will not be descheduled until the hypercall is complete and the ioctl returns to user space. These long running tasks may also trigger the kernel's soft lockup detection. Add xen_preemptible_hcall_begin() and xen_preemptible_hcall_end() to bracket hypercalls that may be preempted. Use these in the privcmd driver. When returning from an upcall, call preempt_schedule_irq() if the current task was within a preemptible hypercall. Since preempt_schedule_irq() can move the task to a different CPU, clear and set xen_in_preemptible_hcall around the call. Signed-off-by: David Vrabel --- Changes in v4: - Fix 32-bit build. Changes in v3: - Export xen_in_preemptible_hcall (to fix modular privcmd driver). Changes in v2: - Use per-cpu variable to mark preemptible regions - Call preempt_schedule_irq() from the correct place in xen_hypervisor_callback --- arch/x86/kernel/entry_32.S | 23 +++++++++++++++++++++++ arch/x86/kernel/entry_64.S | 19 +++++++++++++++++++ drivers/xen/Makefile | 2 +- drivers/xen/preempt.c | 17 +++++++++++++++++ drivers/xen/privcmd.c | 2 ++ include/xen/xen-ops.h | 27 +++++++++++++++++++++++++++ 6 files changed, 89 insertions(+), 1 deletion(-) create mode 100644 drivers/xen/preempt.c diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index a2a4f46..024578d 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -998,7 +998,30 @@ ENTRY(xen_hypervisor_callback) ENTRY(xen_do_upcall) 1: mov %esp, %eax call xen_evtchn_do_upcall +#ifdef CONFIG_PREEMPT jmp ret_from_intr +#else + GET_THREAD_INFO(%ebp) +#ifdef CONFIG_VM86 + movl PT_EFLAGS(%esp), %eax # mix EFLAGS and CS + movb PT_CS(%esp), %al + andl $(X86_EFLAGS_VM | SEGMENT_RPL_MASK), %eax +#else + movl PT_CS(%esp), %eax + andl $SEGMENT_RPL_MASK, %eax +#endif + cmpl $USER_RPL, %eax + jae resume_userspace # returning to v8086 or userspace + DISABLE_INTERRUPTS(CLBR_ANY) + cmpl $0,PER_CPU_VAR(__preempt_count) + jnz resume_kernel + cmpb $0,PER_CPU_VAR(xen_in_preemptible_hcall) + jz resume_kernel + movb $0,PER_CPU_VAR(xen_in_preemptible_hcall) + call preempt_schedule_irq + movb $1,PER_CPU_VAR(xen_in_preemptible_hcall) + jmp resume_kernel +#endif /* CONFIG_PREEMPT */ CFI_ENDPROC ENDPROC(xen_hypervisor_callback) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 1e96c36..d8f4fd8 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1404,7 +1404,25 @@ ENTRY(xen_do_hypervisor_callback) # do_hypervisor_callback(struct *pt_regs) popq %rsp CFI_DEF_CFA_REGISTER rsp decl PER_CPU_VAR(irq_count) +#ifdef CONFIG_PREEMPT jmp error_exit +#else + movl %ebx, %eax + RESTORE_REST + DISABLE_INTERRUPTS(CLBR_NONE) + TRACE_IRQS_OFF + GET_THREAD_INFO(%rcx) + testl %eax, %eax + je error_exit_user + cmpl $0,PER_CPU_VAR(__preempt_count) + jnz retint_kernel + cmpb $0,PER_CPU_VAR(xen_in_preemptible_hcall) + jz retint_kernel + movb $0,PER_CPU_VAR(xen_in_preemptible_hcall) + call preempt_schedule_irq + movb $1,PER_CPU_VAR(xen_in_preemptible_hcall) + jmp retint_kernel +#endif CFI_ENDPROC END(xen_do_hypervisor_callback) @@ -1629,6 +1647,7 @@ ENTRY(error_exit) GET_THREAD_INFO(%rcx) testl %eax,%eax jne retint_kernel +error_exit_user: LOCKDEP_SYS_EXIT_IRQ movl TI_flags(%rcx),%edx movl $_TIF_WORK_MASK,%edi diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile index 45e00af..6b867e9 100644 --- a/drivers/xen/Makefile +++ b/drivers/xen/Makefile @@ -2,7 +2,7 @@ ifeq ($(filter y, $(CONFIG_ARM) $(CONFIG_ARM64)),) obj-$(CONFIG_HOTPLUG_CPU) += cpu_hotplug.o endif obj-$(CONFIG_X86) += fallback.o -obj-y += grant-table.o features.o balloon.o manage.o +obj-y += grant-table.o features.o balloon.o manage.o preempt.o obj-y += events/ obj-y += xenbus/ diff --git a/drivers/xen/preempt.c b/drivers/xen/preempt.c new file mode 100644 index 0000000..b5a3e98 --- /dev/null +++ b/drivers/xen/preempt.c @@ -0,0 +1,17 @@ +/* + * Preemptible hypercalls + * + * Copyright (C) 2014 Citrix Systems R&D ltd. + * + * This source code is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of the + * License, or (at your option) any later version. + */ + +#include + +#ifndef CONFIG_PREEMPT +DEFINE_PER_CPU(bool, xen_in_preemptible_hcall); +EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall); +#endif diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c index 569a13b..59ac71c 100644 --- a/drivers/xen/privcmd.c +++ b/drivers/xen/privcmd.c @@ -56,10 +56,12 @@ static long privcmd_ioctl_hypercall(void __user *udata) if (copy_from_user(&hypercall, udata, sizeof(hypercall))) return -EFAULT; + xen_preemptible_hcall_begin(); ret = privcmd_call(hypercall.op, hypercall.arg[0], hypercall.arg[1], hypercall.arg[2], hypercall.arg[3], hypercall.arg[4]); + xen_preemptible_hcall_end(); return ret; } diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h index fb2ea8f..6d8c042 100644 --- a/include/xen/xen-ops.h +++ b/include/xen/xen-ops.h @@ -35,4 +35,31 @@ int xen_unmap_domain_mfn_range(struct vm_area_struct *vma, int numpgs, struct page **pages); bool xen_running_on_version_or_later(unsigned int major, unsigned int minor); + +#ifdef CONFIG_PREEMPT + +static inline void xen_preemptible_hcall_begin(void) +{ +} + +static inline void xen_preemptible_hcall_end(void) +{ +} + +#else + +DECLARE_PER_CPU(bool, xen_in_preemptible_hcall); + +static inline void xen_preemptible_hcall_begin(void) +{ + __this_cpu_write(xen_in_preemptible_hcall, true); +} + +static inline void xen_preemptible_hcall_end(void) +{ + __this_cpu_write(xen_in_preemptible_hcall, false); +} + +#endif /* CONFIG_PREEMPT */ + #endif /* INCLUDE_XEN_OPS_H */ -- 1.7.10.4