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Message-ID: <alpine.DEB.2.02.1509071732500.2672@kaball.uk.xensource.com>
Date: Mon, 7 Sep 2015 17:39:09 +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 v4 12/20] xen/balloon: Don't rely on the page granularity
is the same for Xen and Linux
On Mon, 7 Sep 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 granularity, a single page will be spread over multiple
> Xen frame.
>
> To avoid splitting the page into 4K frame, take advantage of the
> extent_order field to directly allocate/free chunk of the Linux page
> size.
>
> Note that PVMMU is only used for PV guest (which is x86) and the page
> granularity is always 4KB. Some BUILD_BUG_ON has been added to ensure
> that because the code has not been modified.
>
> Signed-off-by: Julien Grall <julien.grall@...rix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@...citrix.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>
>
> Note that two BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE) in code built
> for the PV MMU code is kept in order to have at least one even if we
> ever decide to drop of code section.
>
> Changes in v4:
> - s/xen_page_to_pfn/page_to_xen_pfn/ based on the new naming
> - Use the field lru in the page to get a list of pages when
> decreasing the memory reservation. It avoids to use a static
> array to store the pages (see v3).
> - Update comment for EXTENT_ORDER.
>
> Changes in v3:
> - Fix errors reported by checkpatch.pl
> - s/mfn/gfn/ based on the new naming
> - Rather than splitting the page into 4KB chunk, use the
> extent_order field to allocate directly a Linux page size. This
> is avoid lots of code for no benefits.
>
> 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 | 59 ++++++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 44 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index c79329f..3babf13 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -70,6 +70,11 @@
> #include <xen/features.h>
> #include <xen/page.h>
>
> +/* Use one extent per PAGE_SIZE to avoid to break down the page into
> + * multiple frame.
> + */
> +#define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
> +
> /*
> * balloon_process() state:
> *
> @@ -230,6 +235,11 @@ static enum bp_state reserve_additional_memory(long credit)
> nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
>
> #ifdef CONFIG_XEN_HAVE_PVMMU
> + /* We don't support PV MMU when Linux and Xen is using
> + * different page granularity.
> + */
> + BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
> +
> /*
> * add_memory() will build page tables for the new memory so
> * the p2m must contain invalid entries so the correct
> @@ -326,11 +336,11 @@ static enum bp_state reserve_additional_memory(long credit)
> static enum bp_state increase_reservation(unsigned long nr_pages)
> {
> int rc;
> - unsigned long pfn, i;
> + unsigned long i;
> struct page *page;
> struct xen_memory_reservation reservation = {
> .address_bits = 0,
> - .extent_order = 0,
> + .extent_order = EXTENT_ORDER,
> .domid = DOMID_SELF
> };
>
> @@ -352,7 +362,11 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
> nr_pages = i;
> break;
> }
> - frame_list[i] = page_to_pfn(page);
> +
> + /* XENMEM_populate_physmap requires a PFN based on Xen
> + * granularity.
> + */
> + frame_list[i] = page_to_xen_pfn(page);
> page = balloon_next_page(page);
> }
>
> @@ -366,10 +380,15 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
> page = balloon_retrieve(false);
> BUG_ON(page == NULL);
>
> - pfn = page_to_pfn(page);
> -
> #ifdef CONFIG_XEN_HAVE_PVMMU
> + /* We don't support PV MMU when Linux and Xen is using
> + * different page granularity.
> + */
> + BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
> +
> if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> + unsigned long pfn = page_to_pfn(page);
> +
> set_phys_to_machine(pfn, frame_list[i]);
>
> /* Link back into the page tables if not highmem. */
> @@ -396,14 +415,15 @@ 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;
> - struct page *page;
> + unsigned long i;
> + struct page *page, *tmp;
> int ret;
> struct xen_memory_reservation reservation = {
> .address_bits = 0,
> - .extent_order = 0,
> + .extent_order = EXTENT_ORDER,
> .domid = DOMID_SELF
> };
> + LIST_HEAD(pages);
>
> #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
> if (balloon_stats.hotplug_pages) {
> @@ -425,8 +445,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> break;
> }
> scrub_page(page);
> -
> - frame_list[i] = page_to_pfn(page);
> + list_add(&page->lru, &pages);
> }
>
> /*
> @@ -438,14 +457,23 @@ 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. */
> - for (i = 0; i < nr_pages; i++) {
> - pfn = frame_list[i];
> - frame_list[i] = pfn_to_gfn(pfn);
> - page = pfn_to_page(pfn);
> + /*
> + * Setup the frame, update direct mapping, invalidate P2M,
> + * and add to balloon.
> + */
> + list_for_each_entry_safe(page, tmp, &pages, lru) {
> + /* XENMEM_decrease_reservation requires a GFN */
> + frame_list[i] = xen_page_to_gfn(page);
>
> #ifdef CONFIG_XEN_HAVE_PVMMU
> + /* We don't support PV MMU when Linux and Xen is using
> + * different page granularity.
> + */
> + BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
> +
> if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> + unsigned long pfn = page_to_pfn(page);
> +
> if (!PageHighMem(page)) {
> ret = HYPERVISOR_update_va_mapping(
> (unsigned long)__va(pfn << PAGE_SHIFT),
> @@ -455,6 +483,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
> __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
> }
> #endif
> + list_del(&page->lru);
>
> balloon_append(page);
> }
> --
> 2.1.4
>
--
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