xen: allow more than 512 GB of RAM for 64 bit pv-domains

64 bit pv-domains under Xen are limited to 512 GB of RAM today. The
main reason has been the 3 level p2m tree, which was replaced by the
virtual mapped linear p2m list. Parallel to the p2m list which is
being used by the kernel itself there is a 3 level mfn tree for usage
by the Xen tools and eventually for crash dump analysis. For this tree
the linear p2m list can serve as a replacement, too. As the kernel
can't know whether the tools are capable of dealing with the p2m list
instead of the mfn tree, the limit of 512 GB can't be dropped in all
cases.

This patch replaces the hard limit by a kernel parameter which tells
the kernel to obey the 512 GB limit or not. The default is selected by
a configuration parameter which specifies whether the 512 GB limit
should be active per default for domUs (domain save/restore/migration
and crash dump analysis are affected).

Memory above the domain limit is returned to the hypervisor instead of
being identity mapped, which was wrong anyway.

The kernel configuration parameter to specify the maximum size of a
domain can be deleted, as it is not relevant any more.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Konrad Rzeszutek Wilk <Konrad.wilk@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 50 insertions, 9 deletions

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index b096d02d34ac..f96002107691 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -33,6 +33,8 @@
 #include "p2m.h"
 #include "mmu.h"
 
+#define GB(x) ((uint64_t)(x) * 1024 * 1024 * 1024)
+
 /* Amount of extra memory space we add to the e820 ranges */
 struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
 
@@ -69,6 +71,26 @@ static unsigned long xen_remap_mfn __initdata = INVALID_P2M_ENTRY;
  */
 #define EXTRA_MEM_RATIO		(10)
 
+static bool xen_512gb_limit __initdata = IS_ENABLED(CONFIG_XEN_512GB);
+
+static void __init xen_parse_512gb(void)
+{
+	bool val = false;
+	char *arg;
+
+	arg = strstr(xen_start_info->cmd_line, "xen_512gb_limit");
+	if (!arg)
+		return;
+
+	arg = strstr(xen_start_info->cmd_line, "xen_512gb_limit=");
+	if (!arg)
+		val = true;
+	else if (strtobool(arg + strlen("xen_512gb_limit="), &val))
+		return;
+
+	xen_512gb_limit = val;
+}
+
 static void __init xen_add_extra_mem(phys_addr_t start, phys_addr_t size)
 {
 	int i;
@@ -503,12 +525,29 @@ void __init xen_remap_memory(void)
 	pr_info("Remapped %ld page(s)\n", remapped);
 }
 
+static unsigned long __init xen_get_pages_limit(void)
+{
+	unsigned long limit;
+
+#ifdef CONFIG_X86_32
+	limit = GB(64) / PAGE_SIZE;
+#else
+	limit = ~0ul;
+	if (!xen_initial_domain() && xen_512gb_limit)
+		limit = GB(512) / PAGE_SIZE;
+#endif
+	return limit;
+}
+
 static unsigned long __init xen_get_max_pages(void)
 {
-	unsigned long max_pages = MAX_DOMAIN_PAGES;
+	unsigned long max_pages, limit;
 	domid_t domid = DOMID_SELF;
 	int ret;
 
+	limit = xen_get_pages_limit();
+	max_pages = limit;
+
 	/*
 	 * For the initial domain we use the maximum reservation as
 	 * the maximum page.
@@ -524,7 +563,7 @@ static unsigned long __init xen_get_max_pages(void)
 			max_pages = ret;
 	}
 
-	return min(max_pages, MAX_DOMAIN_PAGES);
+	return min(max_pages, limit);
 }
 
 static void __init xen_align_and_add_e820_region(phys_addr_t start,
@@ -699,7 +738,7 @@ static void __init xen_reserve_xen_mfnlist(void)
  **/
 char * __init xen_memory_setup(void)
 {
-	unsigned long max_pfn = xen_start_info->nr_pages;
+	unsigned long max_pfn;
 	phys_addr_t mem_end, addr, size, chunk_size;
 	u32 type;
 	int rc;
@@ -709,7 +748,9 @@ char * __init xen_memory_setup(void)
 	int i;
 	int op;
 
-	max_pfn = min(MAX_DOMAIN_PAGES, max_pfn);
+	xen_parse_512gb();
+	max_pfn = xen_get_pages_limit();
+	max_pfn = min(max_pfn, xen_start_info->nr_pages);
 	mem_end = PFN_PHYS(max_pfn);
 
 	memmap.nr_entries = E820MAX;
@@ -762,12 +803,15 @@ char * __init xen_memory_setup(void)
 	 * is limited to the max size of lowmem, so that it doesn't
 	 * get completely filled.
 	 *
+	 * Make sure we have no memory above max_pages, as this area
+	 * isn't handled by the p2m management.
+	 *
 	 * In principle there could be a problem in lowmem systems if
 	 * the initial memory is also very large with respect to
 	 * lowmem, but we won't try to deal with that here.
 	 */
-	extra_pages = min(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)),
-			  extra_pages);
+	extra_pages = min3(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)),
+			   extra_pages, max_pages - max_pfn);
 	i = 0;
 	addr = xen_e820_map[0].addr;
 	size = xen_e820_map[0].size;
@@ -803,9 +847,6 @@ char * __init xen_memory_setup(void)
 	/*
 	 * Set the rest as identity mapped, in case PCI BARs are
 	 * located here.
-	 *
-	 * PFNs above MAX_P2M_PFN are considered identity mapped as
-	 * well.
 	 */
 	set_phys_range_identity(addr / PAGE_SIZE, ~0ul);