On Wed, Jan 21, 2015 at 6:17 PM, Luis R. Rodriguez <mcgrof@xxxxxxxxxxxxxxxx> wrote: > From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx> > > On kernels with voluntary or no preemption we can run > into situations where a hypercall issued through userspace > will linger around as it addresses sub-operatiosn in kernel > context (multicalls). Such operations can trigger soft lockup > detection. > > We want to address a way to let the kernel voluntarily preempt > such calls even on non preempt kernels, to address this we first > need to distinguish which hypercalls fall under this category. > This implements xen_is_preemptible_hypercall() which lets us do > just that by adding a secondary hypercall page, calls made via > the new page may be preempted. > > Andrew had originally submitted a version of this work [0]. > > [0] http://lists.xen.org/archives/html/xen-devel/2014-02/msg01056.html > > Based on original work by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> > > Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > Cc: Borislav Petkov <bp@xxxxxxx> > Cc: David Vrabel <david.vrabel@xxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: x86@xxxxxxxxxx > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx> > Cc: Jan Beulich <JBeulich@xxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx > Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx> > --- > arch/x86/include/asm/xen/hypercall.h | 20 ++++++++++++++++++++ > arch/x86/xen/enlighten.c | 7 +++++++ > arch/x86/xen/xen-head.S | 18 +++++++++++++++++- > 3 files changed, 44 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h > index ca08a27..221008e 100644 > --- a/arch/x86/include/asm/xen/hypercall.h > +++ b/arch/x86/include/asm/xen/hypercall.h > @@ -84,6 +84,22 @@ > > extern struct { char _entry[32]; } hypercall_page[]; > > +#ifndef CONFIG_PREEMPT > +extern struct { char _entry[32]; } preemptible_hypercall_page[]; A comment somewhere explaining why only non-preemptible kernels have preemptible hypercalls might be friendly to some future reader. :) > + > +static inline bool xen_is_preemptible_hypercall(struct pt_regs *regs) > +{ > + return !user_mode_vm(regs) && > + regs->ip >= (unsigned long)preemptible_hypercall_page && > + regs->ip < (unsigned long)preemptible_hypercall_page + PAGE_SIZE; > +} This makes it seem like the page is indeed one page long, but I don't see what actually allocates a whole page for it. What am I missing? --Andy -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
