Re: [Xen-devel] [PATCH 1/2] xen: prepare p2m list for memory hotplug

[Juergen Gross <jgross@xxxxxxxx>]

On 03/19/2015 05:14 PM, Daniel Kiper wrote:
> On Thu, Mar 19, 2015 at 03:31:01PM +0100, Juergen Gross wrote:
> > Commit 054954eb051f35e74b75a566a96fe756015352c8 ("xen: switch to linear
> > virtual mapped sparse p2m list") introduced a regression regarding to
> > memory hotplug for a pv-domain: as the virtual space for the p2m list
> > is allocated for the to be expected memory size of the domain only,
> > hotplugged memory above that size will not be usable by the domain.
> >
> > Correct this by using a configurable size for the p2m list in case of
> > memory hotplug enabled (default supported memory size is 512 GB for
> > 64 bit domains and 4 GB for 32 bit domains).
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   arch/x86/xen/p2m.c  | 13 ++++++++++++-
> >   drivers/xen/Kconfig | 13 +++++++++++++
> >   2 files changed, 25 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> > index 9f93af5..30e84ae 100644
> > --- a/arch/x86/xen/p2m.c
> > +++ b/arch/x86/xen/p2m.c
> > @@ -91,6 +91,17 @@ EXPORT_SYMBOL_GPL(xen_p2m_size);
> >   unsigned long xen_max_p2m_pfn __read_mostly;
> >   EXPORT_SYMBOL_GPL(xen_max_p2m_pfn);
> >
> > +#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
> > +#ifdef CONFIG_X86_32
> > +BUILD_BUG_ON_MSG(CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT > 64)
> > +#endif
> > +#define P2M_LIMIT max(xen_max_p2m_pfn,                                 \
> > +       ((unsigned long)((u64)CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT * \
> > +       1024 * 1024 * 1024 / PAGE_SIZE)))
> > +#else
> > +#define P2M_LIMIT xen_max_p2m_pfn
> > +#endif
> > +
> >   static DEFINE_SPINLOCK(p2m_update_lock);
> >
> >   static unsigned long *p2m_mid_missing_mfn;
> > @@ -387,7 +398,7 @@ void __init xen_vmalloc_p2m_tree(void)
> >         static struct vm_struct vm;
> >
> >         vm.flags = VM_ALLOC;
> > -       vm.size = ALIGN(sizeof(unsigned long) * xen_max_p2m_pfn,
> > +       vm.size = ALIGN(sizeof(unsigned long) * P2M_LIMIT,
> >                         PMD_SIZE * PMDS_PER_MID_PAGE);
> What happens when somebody will allocate more memory for guest than
> XEN_BALLOON_MEMORY_HOTPLUG_LIMIT? Additionally, I think that we do
It will fail to add like it does without this patch.

> not need allocate extra virtual address space if memory hotplug is
> disabled.
As XEN_BALLOON_MEMORY_HOTPLUG_LIMIT depends on
XEN_BALLOON_MEMORY_HOTPLUG which in turn depends on MEMORY_HOTPLUG,
this is already the case.

> >         vm_area_register_early(&vm, PMD_SIZE * PMDS_PER_MID_PAGE);
> >         pr_notice("p2m virtual area at %p, size is %lx\n", vm.addr, vm.size);
> > diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> > index b812462..0a61ddf 100644
> > --- a/drivers/xen/Kconfig
> > +++ b/drivers/xen/Kconfig
> > @@ -55,6 +55,19 @@ config XEN_BALLOON_MEMORY_HOTPLUG
> >
> >           In that case step 3 should be omitted.
> >
> > +config XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
> > +       int
> > +       default 512 if X86_64
> > +       default 4 if X86_32
> > +       depends on XEN_HAVE_PVMMU
> Do we need dependency on XEN_HAVE_PVMMU?
Yes. Needed only for pv domains.

> If yes than maybe "depends on XEN_HAVE_PVMMU && XEN_BALLOON_MEMORY_HOTPLUG".
Matter of taste, I guess.

> > +       depends on XEN_BALLOON_MEMORY_HOTPLUG
> Should not this option be available even when memory hotplug is disabled?
Why?


Juergen

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