Re: [RFC PATCH 10/16] xen/balloon: support ballooning in xenhost_t

[Ankur Arora]

On 6/17/19 2:28 AM, Juergen Gross wrote:
> On 09.05.19 19:25, Ankur Arora wrote:
> > Xen ballooning uses hollow struct pages (with the underlying GFNs being
> > populated/unpopulated via hypercalls) which are used by the grant logic
> > to map grants from other domains.
> >
> > This patch allows the default xenhost to provide an alternate ballooning
> > allocation mechanism. This is expected to be useful for local xenhosts
> > (type xenhost_r0) because unlike Xen, where there is an external
> > hypervisor which can change the memory underneath a GFN, that is not
> > possible when the hypervisor is running in the same address space
> > as the entity doing the ballooning.
> >
> > Co-developed-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
> > Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
> > Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
> > ---
> > Â arch/x86/xen/enlighten_hvm.cÂÂÂÂÂÂ |Â 7 +++++++
> > Â arch/x86/xen/enlighten_pv.cÂÂÂÂÂÂÂ |Â 8 ++++++++
> > Â drivers/xen/balloon.cÂÂÂÂÂÂÂÂÂÂÂÂÂ | 19 ++++++++++++++++---
> > Â drivers/xen/grant-table.cÂÂÂÂÂÂÂÂÂ |Â 4 ++--
> > Â drivers/xen/privcmd.cÂÂÂÂÂÂÂÂÂÂÂÂÂ |Â 4 ++--
> > Â drivers/xen/xen-selfballoon.cÂÂÂÂÂ |Â 2 ++
> > Â drivers/xen/xenbus/xenbus_client.c |Â 6 +++---
> > Â drivers/xen/xlate_mmu.cÂÂÂÂÂÂÂÂÂÂÂ |Â 4 ++--
> > Â include/xen/balloon.hÂÂÂÂÂÂÂÂÂÂÂÂÂ |Â 4 ++--
> > Â include/xen/xenhost.hÂÂÂÂÂÂÂÂÂÂÂÂÂ | 19 +++++++++++++++++++
> > Â 10 files changed, 63 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> > index 5ef4d6ad920d..08becf574743 100644
> > --- a/drivers/xen/balloon.c
> > +++ b/drivers/xen/balloon.c
> > @@ -63,6 +63,7 @@
> > Â #include <asm/tlb.h>
> > Â #include <xen/interface/xen.h>
> > +#include <xen/xenhost.h>
> > Â #include <asm/xen/hypervisor.h>
> > Â #include <asm/xen/hypercall.h>
> > @@ -583,12 +584,21 @@ static int add_ballooned_pages(int nr_pages)
> > ÂÂ * @pages: pages returned
> > ÂÂ * @return 0 on success, error otherwise
> > ÂÂ */
> > -int alloc_xenballooned_pages(int nr_pages, struct page **pages)
> > +int alloc_xenballooned_pages(xenhost_t *xh, int nr_pages, struct page 
> > **pages)
> > Â {
> > ÂÂÂÂÂ int pgno = 0;
> > ÂÂÂÂÂ struct page *page;
> > ÂÂÂÂÂ int ret;
> > +ÂÂÂ /*
> > +ÂÂÂÂ * xenmem transactions for remote xenhost are disallowed.
> > +ÂÂÂÂ */
> > +ÂÂÂ if (xh->type == xenhost_r2)
> > +ÂÂÂÂÂÂÂ return -EINVAL;
>
> Why don't you set a dummy function returning -EINVAL into the xenhost_r2
> structure instead?
Will do. And, same for the two comments below.

Ankur

> > +
> > +ÂÂÂ if (xh->ops->alloc_ballooned_pages)
> > +ÂÂÂÂÂÂÂ return xh->ops->alloc_ballooned_pages(xh, nr_pages, pages);
> > +
>
> Please make alloc_xenballooned_pages() an inline wrapper and use the
> current implmentaion as the default. This avoids another if ().
>
> > ÂÂÂÂÂ mutex_lock(&balloon_mutex);
> > ÂÂÂÂÂ balloon_stats.target_unpopulated += nr_pages;
> > @@ -620,7 +630,7 @@ int alloc_xenballooned_pages(int nr_pages, struct 
> > page **pages)
> > ÂÂÂÂÂ return 0;
> > ÂÂ out_undo:
> > ÂÂÂÂÂ mutex_unlock(&balloon_mutex);
> > -ÂÂÂ free_xenballooned_pages(pgno, pages);
> > +ÂÂÂ free_xenballooned_pages(xh, pgno, pages);
> > ÂÂÂÂÂ return ret;
> > Â }
> > Â EXPORT_SYMBOL(alloc_xenballooned_pages);
> > @@ -630,10 +640,13 @@ EXPORT_SYMBOL(alloc_xenballooned_pages);
> > ÂÂ * @nr_pages: Number of pages
> > ÂÂ * @pages: pages to return
> > ÂÂ */
> > -void free_xenballooned_pages(int nr_pages, struct page **pages)
> > +void free_xenballooned_pages(xenhost_t *xh, int nr_pages, struct page 
> > **pages)
> > Â {
> > ÂÂÂÂÂ int i;
> > +ÂÂÂ if (xh->ops->free_ballooned_pages)
> > +ÂÂÂÂÂÂÂ return xh->ops->free_ballooned_pages(xh, nr_pages, pages);
> > +
>
> Same again: please use an inline wrapper.
>
>
> Juergen