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Message-ID: <alpine.DEB.2.02.1507161819200.17378@kaball.uk.xensource.com>
Date: Fri, 17 Jul 2015 15:03:39 +0100
From: Stefano Stabellini <stefano.stabellini@...citrix.com>
To: Julien Grall <julien.grall@...rix.com>
CC: <xen-devel@...ts.xenproject.org>,
<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
"David Vrabel" <david.vrabel@...rix.com>,
Wei Liu <wei.liu2@...rix.com>
Subject: Re: [PATCH v2 12/20] xen/balloon: Don't rely on the page granularity
is the same for Xen and Linux
On Thu, 9 Jul 2015, Julien Grall wrote:
> For ARM64 guests, Linux is able to support either 64K or 4K page
> granularity. Although, the hypercall interface is always based on 4K
> page granularity.
>
> With 64K page granuliarty, a single page will be spread over multiple
> Xen frame.
>
> When a driver request/free a balloon page, the balloon driver will have
> to split the Linux page in 4K chunk before asking Xen to add/remove the
> frame from the guest.
>
> Note that this can work on any page granularity assuming it's a multiple
> of 4K.
>
> Signed-off-by: Julien Grall <julien.grall@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: Wei Liu <wei.liu2@...rix.com>
> ---
> Changes in v2:
> - Use xen_apply_to_page to split a page in 4K chunk
> - It's not necessary to have a smaller frame list. Re-use
> PAGE_SIZE
> - Convert reserve_additional_memory to use XEN_... macro
> ---
> drivers/xen/balloon.c | 147 +++++++++++++++++++++++++++++++++++---------------
> 1 file changed, 105 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index fd93369..19a72b1 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -230,6 +230,7 @@ static enum bp_state reserve_additional_memory(long credit)
> nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
>
> #ifdef CONFIG_XEN_HAVE_PVMMU
> + /* TODO */
I think you need to be more verbose than that: TODO what?
> /*
> * add_memory() will build page tables for the new memory so
> * the p2m must contain invalid entries so the correct
> @@ -242,8 +243,8 @@ static enum bp_state reserve_additional_memory(long credit)
> if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> unsigned long pfn, i;
>
> - pfn = PFN_DOWN(hotplug_start_paddr);
> - for (i = 0; i < balloon_hotplug; i++) {
> + pfn = XEN_PFN_DOWN(hotplug_start_paddr);
> + for (i = 0; i < (balloon_hotplug * XEN_PFN_PER_PAGE); i++) {
> if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
> pr_warn("set_phys_to_machine() failed, no memory added\n");
> return BP_ECANCELED;
> @@ -323,10 +324,72 @@ static enum bp_state reserve_additional_memory(long credit)
> }
> #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
>
> +static int set_frame(struct page *page, unsigned long pfn, void *data)
> +{
> + unsigned long *index = data;
> +
> + frame_list[(*index)++] = pfn;
> +
> + return 0;
> +}
> +
> +#ifdef CONFIG_XEN_HAVE_PVMMU
> +static int pvmmu_update_mapping(struct page *page, unsigned long pfn,
> + void *data)
> +{
> + unsigned long *index = data;
> + xen_pfn_t frame = frame_list[*index];
> +
> + set_phys_to_machine(pfn, frame);
> + /* Link back into the page tables if not highmem. */
> + if (!PageHighMem(page)) {
> + int ret;
> + ret = HYPERVISOR_update_va_mapping(
> + (unsigned long)__va(pfn << XEN_PAGE_SHIFT),
> + mfn_pte(frame, PAGE_KERNEL),
> + 0);
> + BUG_ON(ret);
> + }
> +
> + (*index)++;
> +
> + return 0;
> +}
> +#endif
> +
> +static int balloon_remove_mapping(struct page *page, unsigned long pfn,
> + void *data)
> +{
> + unsigned long *index = data;
> +
> + /* We expect the frame_list to contain the same pfn */
> + BUG_ON(pfn != frame_list[*index]);
> +
> + frame_list[*index] = pfn_to_mfn(pfn);
> +
> +#ifdef CONFIG_XEN_HAVE_PVMMU
> + if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> + if (!PageHighMem(page)) {
> + int ret;
> +
> + ret = HYPERVISOR_update_va_mapping(
> + (unsigned long)__va(pfn << XEN_PAGE_SHIFT),
> + __pte_ma(0), 0);
> + BUG_ON(ret);
> + }
> + __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
> + }
> +#endif
> +
> + (*index)++;
> +
> + return 0;
> +}
> +
> static enum bp_state increase_reservation(unsigned long nr_pages)
> {
> int rc;
> - unsigned long pfn, i;
> + unsigned long i, frame_idx;
> struct page *page;
> struct xen_memory_reservation reservation = {
> .address_bits = 0,
> @@ -343,44 +406,43 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
> }
> #endif
>
> - if (nr_pages > ARRAY_SIZE(frame_list))
> - nr_pages = ARRAY_SIZE(frame_list);
> + if (nr_pages > (ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE))
> + nr_pages = ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE;
>
> + frame_idx = 0;
> page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
> for (i = 0; i < nr_pages; i++) {
> if (!page) {
> nr_pages = i;
> break;
> }
> - frame_list[i] = page_to_pfn(page);
> +
> + rc = xen_apply_to_page(page, set_frame, &frame_idx);
> +
> page = balloon_next_page(page);
> }
>
> set_xen_guest_handle(reservation.extent_start, frame_list);
> - reservation.nr_extents = nr_pages;
> + reservation.nr_extents = nr_pages * XEN_PFN_PER_PAGE;
> rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
> if (rc <= 0)
> return BP_EAGAIN;
>
> - for (i = 0; i < rc; i++) {
> + /* rc is equal to the number of Xen page populated */
> + nr_pages = rc / XEN_PFN_PER_PAGE;
Here we are purposedly ignoring any spares (rc % XEN_PFN_PER_PAGE).
Instead of leaking them, maybe we should givem them back to Xen since we
cannot use them?
> + for (i = 0; i < nr_pages; i++) {
> page = balloon_retrieve(false);
> BUG_ON(page == NULL);
>
> - pfn = page_to_pfn(page);
> -
> #ifdef CONFIG_XEN_HAVE_PVMMU
> + frame_idx = 0;
Shouldn't this be before the beginning of the loop above?
> if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> - set_phys_to_machine(pfn, frame_list[i]);
> -
> - /* Link back into the page tables if not highmem. */
> - if (!PageHighMem(page)) {
> - int ret;
> - ret = HYPERVISOR_update_va_mapping(
> - (unsigned long)__va(pfn << PAGE_SHIFT),
> - mfn_pte(frame_list[i], PAGE_KERNEL),
> - 0);
> - BUG_ON(ret);
> - }
> + int ret;
> +
> + ret = xen_apply_to_page(page, pvmmu_update_mapping,
> + &frame_idx);
> + BUG_ON(ret);
> }
> #endif
>
> @@ -388,7 +450,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
> __free_reserved_page(page);
> }
>
> - balloon_stats.current_pages += rc;
> + balloon_stats.current_pages += nr_pages;
>
> return BP_DONE;
> }
> @@ -396,7 +458,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
> static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> {
> enum bp_state state = BP_DONE;
> - unsigned long pfn, i;
> + unsigned long pfn, i, frame_idx, nr_frames;
> struct page *page;
> int ret;
> struct xen_memory_reservation reservation = {
> @@ -414,9 +476,10 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> }
> #endif
>
> - if (nr_pages > ARRAY_SIZE(frame_list))
> - nr_pages = ARRAY_SIZE(frame_list);
> + if (nr_pages > (ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE))
> + nr_pages = ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE;
>
> + frame_idx = 0;
> for (i = 0; i < nr_pages; i++) {
> page = alloc_page(gfp);
> if (page == NULL) {
> @@ -426,9 +489,12 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> }
> scrub_page(page);
>
> - frame_list[i] = page_to_pfn(page);
> + ret = xen_apply_to_page(page, set_frame, &frame_idx);
> + BUG_ON(ret);
> }
>
> + nr_frames = nr_pages * XEN_PFN_PER_PAGE;
> +
> /*
> * Ensure that ballooned highmem pages don't have kmaps.
> *
> @@ -439,22 +505,19 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> kmap_flush_unused();
>
> /* Update direct mapping, invalidate P2M, and add to balloon. */
> + frame_idx = 0;
> for (i = 0; i < nr_pages; i++) {
> - pfn = frame_list[i];
> - frame_list[i] = pfn_to_mfn(pfn);
> - page = pfn_to_page(pfn);
> + /*
> + * The Xen PFN for a given Linux Page are contiguous in
> + * frame_list
> + */
> + pfn = frame_list[frame_idx];
> + page = xen_pfn_to_page(pfn);
>
> -#ifdef CONFIG_XEN_HAVE_PVMMU
> - if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> - if (!PageHighMem(page)) {
> - ret = HYPERVISOR_update_va_mapping(
> - (unsigned long)__va(pfn << PAGE_SHIFT),
> - __pte_ma(0), 0);
> - BUG_ON(ret);
> - }
> - __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
> - }
> -#endif
> +
> + ret = xen_apply_to_page(page, balloon_remove_mapping,
> + &frame_idx);
> + BUG_ON(ret);
>
> balloon_append(page);
> }
> @@ -462,9 +525,9 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> flush_tlb_all();
>
> set_xen_guest_handle(reservation.extent_start, frame_list);
> - reservation.nr_extents = nr_pages;
> + reservation.nr_extents = nr_frames;
> ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
> - BUG_ON(ret != nr_pages);
> + BUG_ON(ret != nr_frames);
>
> balloon_stats.current_pages -= nr_pages;
>
> --
> 2.1.4
>
--
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