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| author | David Vrabel <david.vrabel@citrix.com> | 2015-02-19 15:23:17 +0000 |
|---|---|---|
| committer | Sasha Levin <sasha.levin@oracle.com> | 2015-07-20 21:12:45 -0400 |
| commit | 54f642ea6676705893c34a0bf53880aea29a1363 (patch) | |
| tree | 6328660dced2736e240b49af38da6be5ccbd07f4 /arch | |
| parent | c35f0b5937875df73c8ca6cdffe38c668ae2a686 (diff) | |
| download | lwn-54f642ea6676705893c34a0bf53880aea29a1363.tar.gz lwn-54f642ea6676705893c34a0bf53880aea29a1363.zip | |
x86/xen: allow privcmd hypercalls to be preempted
[ Upstream commit db0e2aa47f0a45fc56592c25ad370f8836cbb128 ]
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 xen_maybe_preempt_hcall() which
adds a schedule point if if the current task was within a preemptible
hypercall.
Since _cond_resched() can move the task to a different CPU, clear and
set xen_in_preemptible_hcall around the call.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/entry_32.S | 3 | ||||
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 3 |
2 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 344b63f18d14..3dddb89ba320 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -982,6 +982,9 @@ ENTRY(xen_hypervisor_callback) ENTRY(xen_do_upcall) 1: mov %esp, %eax call xen_evtchn_do_upcall +#ifndef CONFIG_PREEMPT + call xen_maybe_preempt_hcall +#endif jmp ret_from_intr CFI_ENDPROC ENDPROC(xen_hypervisor_callback) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index f1dc27f457f1..e36d9815ef56 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1173,6 +1173,9 @@ ENTRY(xen_do_hypervisor_callback) # do_hypervisor_callback(struct *pt_regs) popq %rsp CFI_DEF_CFA_REGISTER rsp decl PER_CPU_VAR(irq_count) +#ifndef CONFIG_PREEMPT + call xen_maybe_preempt_hcall +#endif jmp error_exit CFI_ENDPROC END(xen_do_hypervisor_callback) |