Re: [Xen-devel] [PATCH v1 6/8]: PVH ballooning and grant changes

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 21 Sep 2012, Mukesh Rathor wrote:
> ---
>  drivers/xen/balloon.c     |   35 ++++++++++++++++++++++++++++-------
>  drivers/xen/gntdev.c      |    3 ++-
>  drivers/xen/grant-table.c |   25 +++++++++++++++++++++----
>  3 files changed, 51 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 31ab82f..85a6917 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -358,10 +358,21 @@ static enum bp_state increase_reservation(unsigned long 
> nr_pages)
>               BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
>                      phys_to_machine_mapping_valid(pfn));
>  
> -             set_phys_to_machine(pfn, frame_list[i]);
> +             if (xen_pv_domain() && 
> +                 xen_feature(XENFEAT_auto_translated_physmap)) {
> +                     /* PVH: we just need to update native page table */
> +                     pte_t *ptep;
> +                     unsigned int level;
> +                     void *addr = __va(pfn << PAGE_SHIFT);
> +                     ptep = lookup_address((unsigned long)addr, &level);
> +                     set_pte(ptep, pfn_pte(pfn, PAGE_KERNEL));
> +             } else
> +                     set_phys_to_machine(pfn, frame_list[i]);



>               /* Link back into the page tables if not highmem. */
> -             if (xen_pv_domain() && !PageHighMem(page)) {
> +             if (xen_pv_domain() && !PageHighMem(page) && 
> +                 !xen_feature(XENFEAT_auto_translated_physmap)) {
> +
>                       int ret;
>                       ret = HYPERVISOR_update_va_mapping(
>                               (unsigned long)__va(pfn << PAGE_SHIFT),
> @@ -418,12 +429,21 @@ static enum bp_state decrease_reservation(unsigned long 
> nr_pages, gfp_t gfp)
>               scrub_page(page);
>  
>               if (xen_pv_domain() && !PageHighMem(page)) {
> -                     ret = HYPERVISOR_update_va_mapping(
> -                             (unsigned long)__va(pfn << PAGE_SHIFT),
> -                             __pte_ma(0), 0);
> -                     BUG_ON(ret);
> +                     if (xen_feature(XENFEAT_auto_translated_physmap)) {
> +                             unsigned int level;
> +                             pte_t *ptep;
> +                             void *addr = __va(pfn << PAGE_SHIFT);
> +                             ptep = lookup_address((unsigned long)addr, 
> +                                                     &level);
> +                             set_pte(ptep, __pte(0));
> +
> +                     } else {
> +                             ret = HYPERVISOR_update_va_mapping(
> +                                     (unsigned long)__va(pfn << PAGE_SHIFT),
> +                                     __pte_ma(0), 0);
> +                             BUG_ON(ret);
> +                     }
>               }
> -
>       }
>  
>       /* Ensure that ballooned highmem pages don't have kmaps. */
> @@ -433,6 +453,7 @@ static enum bp_state decrease_reservation(unsigned long 
> nr_pages, gfp_t gfp)
>       /* No more mappings: invalidate P2M and add to balloon. */
>       for (i = 0; i < nr_pages; i++) {
>               pfn = mfn_to_pfn(frame_list[i]);
> +             /* PVH note: following will noop for auto translated */
>               __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
>               balloon_append(pfn_to_page(pfn));
>       }

Maybe we need a function "update_mapping" internal to balloon.c that
would be set to HYPERVISOR_update_va_mapping for pv guests, set_pte for
pvh guests and nothing for pv on hvm guests.

Speaking of which, why do pvh guests need a set_pte while pv on hvm
guests don't? I would think that their behaviour should be the same
regarding ballooning.


> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 1ffd03b..35d1e3c 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -802,7 +802,8 @@ static int __init gntdev_init(void)
>       if (!xen_domain())
>               return -ENODEV;
>  
> -     use_ptemod = xen_pv_domain();
> +     use_ptemod = xen_pv_domain() && 
> +                  !xen_feature(XENFEAT_auto_translated_physmap);
>  
>       err = misc_register(&gntdev_miscdev);
>       if (err != 0) {
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 0bfc1ef..d831d52 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -974,14 +974,19 @@ static void gnttab_unmap_frames_v2(void)
>  static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
>  {
>       struct gnttab_setup_table setup;
> -     unsigned long *frames;
> +     unsigned long *frames, start_gpfn;
>       unsigned int nr_gframes = end_idx + 1;
>       int rc;
>  
> -     if (xen_hvm_domain()) {
> +     if (xen_hvm_domain() || xen_feature(XENFEAT_auto_translated_physmap)) {
>               struct xen_add_to_physmap xatp;
>               unsigned int i = end_idx;
>               rc = 0;
> +
> +             if (xen_hvm_domain())
> +                     start_gpfn = xen_hvm_resume_frames >> PAGE_SHIFT;
> +             else
> +                     start_gpfn = virt_to_pfn(gnttab_shared.addr);
>               /*
>                * Loop backwards, so that the first hypercall has the largest
>                * index, ensuring that the table will grow only once.
> @@ -990,7 +995,7 @@ static int gnttab_map(unsigned int start_idx, unsigned 
> int end_idx)
>                       xatp.domid = DOMID_SELF;
>                       xatp.idx = i;
>                       xatp.space = XENMAPSPACE_grant_table;
> -                     xatp.gpfn = (xen_hvm_resume_frames >> PAGE_SHIFT) + i;
> +                     xatp.gpfn = start_gpfn + i;
>                       rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
>                       if (rc != 0) {
>                               printk(KERN_WARNING
> @@ -1053,7 +1058,7 @@ static void gnttab_request_version(void)
>       int rc;
>       struct gnttab_set_version gsv;
>  
> -     if (xen_hvm_domain())
> +     if (xen_hvm_domain() || xen_feature(XENFEAT_auto_translated_physmap))
>               gsv.version = 1;
>       else
>               gsv.version = 2;
> @@ -1081,12 +1086,24 @@ static void gnttab_request_version(void)
>  int gnttab_resume(void)
>  {
>       unsigned int max_nr_gframes;
> +     char *kmsg="Failed to kmalloc pages for pv in hvm grant frames\n";
>  
>       gnttab_request_version();
>       max_nr_gframes = gnttab_max_grant_frames();
>       if (max_nr_gframes < nr_grant_frames)
>               return -ENOSYS;
>  
> +     /* PVH note: xen will free existing kmalloc'd mfn in 
> +      * XENMEM_add_to_physmap */
> +     if (xen_pv_domain() && xen_feature(XENFEAT_auto_translated_physmap) && 
> +         !gnttab_shared.addr) {
> +             gnttab_shared.addr =
> +                     kmalloc(max_nr_gframes * PAGE_SIZE, GFP_KERNEL);
> +             if ( !gnttab_shared.addr ) {
> +                     printk(KERN_WARNING "%s", kmsg);
> +                     return -ENOMEM;
> +             }
> +     }

the way PVH guests use gnttab_shared.addr is very similar to the way PV
on HVM guests use xen_hvm_resume_frames, except that
xen_hvm_resume_frames is allocated using alloc_xen_mmio instead of
kmalloc.

I wonder if it would produce better code switching PV on HVM guests to
gnttab_shared.addr too (or PVH guests to xen_hvm_resume_frames, but then
xen_hvm_resume_frames would need to be renamed).

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