[PATCH 4/4] EFI: free unused boot mem in at least some cases

[Jan Beulich <jbeulich@suse.com>]

Address at least the primary reason why 52bba67f8b87 ("efi/boot: Don't
free ebmalloc area at all") was put in place: Make xen_in_range() aware
of the freed range. This is in particular relevant for EFI-enabled
builds not actually running on EFI, as the entire range will be unused
in this case.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
The remaining issue could be addressed too, by making the area 2M in
size and 2M-aligned.

--- a/xen/arch/x86/efi/stub.c
+++ b/xen/arch/x86/efi/stub.c
@@ -52,6 +52,12 @@ bool efi_enabled(unsigned int feature)
 
 void __init efi_init_memory(void) { }
 
+bool __hwdom_init efi_boot_mem_unused(unsigned long *start, unsigned long *end)
+{
+    *start = *end = (unsigned long)_end;
+    return false;
+}
+
 void efi_update_l4_pgtable(unsigned int l4idx, l4_pgentry_t l4e) { }
 
 bool efi_rs_using_pgtables(void)
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -608,7 +608,7 @@ static void __init kexec_reserve_area(st
 #endif
 }
 
-static inline bool using_2M_mapping(void)
+bool using_2M_mapping(void)
 {
     return !l1_table_offset((unsigned long)__2M_text_end) &&
            !l1_table_offset((unsigned long)__2M_rodata_start) &&
@@ -1970,7 +1970,7 @@ int __hwdom_init xen_in_range(unsigned l
     paddr_t start, end;
     int i;
 
-    enum { region_s3, region_ro, region_rw, nr_regions };
+    enum { region_s3, region_ro, region_rw, region_bss, nr_regions };
     static struct {
         paddr_t s, e;
     } xen_regions[nr_regions] __hwdom_initdata;
@@ -1994,7 +1994,14 @@ int __hwdom_init xen_in_range(unsigned l
         xen_regions[region_ro].e = __pa(&__2M_rodata_end);
         /* hypervisor .data + .bss */
         xen_regions[region_rw].s = __pa(&__2M_rwdata_start);
-        xen_regions[region_rw].e = __pa(&__2M_rwdata_end);
+        if ( efi_boot_mem_unused(&start, &end) )
+        {
+            xen_regions[region_rw].e = __pa(start);
+            xen_regions[region_bss].s = __pa(end);
+            xen_regions[region_bss].e = __pa(&__2M_rwdata_end);
+        }
+        else
+            xen_regions[region_rw].e = __pa(&__2M_rwdata_end);
     }
 
     start = (paddr_t)mfn << PAGE_SHIFT;
--- a/xen/common/efi/ebmalloc.c
+++ b/xen/common/efi/ebmalloc.c
@@ -1,5 +1,9 @@
 #include "efi.h"
 #include <xen/init.h>
+#include <xen/mm.h>
+#ifdef CONFIG_X86
+#include <asm/setup.h>
+#endif
 
 #ifdef CONFIG_ARM
 /*
@@ -21,7 +25,7 @@
 
 static char __section(".bss.page_aligned") __aligned(PAGE_SIZE)
     ebmalloc_mem[EBMALLOC_SIZE];
-static unsigned long __initdata ebmalloc_allocated;
+static unsigned long __read_mostly ebmalloc_allocated;
 
 /* EFI boot allocator. */
 void __init *ebmalloc(size_t size)
@@ -36,17 +40,32 @@ void __init *ebmalloc(size_t size)
     return ptr;
 }
 
+bool __hwdom_init efi_boot_mem_unused(unsigned long *start, unsigned long *end)
+{
+    *start = (unsigned long)ebmalloc_mem + PAGE_ALIGN(ebmalloc_allocated);
+    *end = (unsigned long)ebmalloc_mem + sizeof(ebmalloc_mem);
+
+    return *start < *end;
+}
+
 void __init free_ebmalloc_unused_mem(void)
 {
-#if 0 /* FIXME: Putting a hole in the BSS breaks the IOMMU mappings for dom0. */
     unsigned long start, end;
 
-    start = (unsigned long)ebmalloc_mem + PAGE_ALIGN(ebmalloc_allocated);
-    end = (unsigned long)ebmalloc_mem + sizeof(ebmalloc_mem);
+#ifdef CONFIG_X86
+    /* FIXME: Putting a hole in .bss would shatter the large page mapping. */
+    if ( using_2M_mapping() )
+    {
+        ebmalloc_allocated = sizeof(ebmalloc_mem);
+        return;
+    }
+#endif
+
+    if ( !efi_boot_mem_unused(&start, &end) )
+        return;
 
     destroy_xen_mappings(start, end);
     init_xenheap_pages(__pa(start), __pa(end));
 
     printk(XENLOG_INFO "Freed %lukB unused BSS memory\n", (end - start) >> 10);
-#endif
 }
--- a/xen/include/asm-x86/setup.h
+++ b/xen/include/asm-x86/setup.h
@@ -9,6 +9,8 @@ extern const char __2M_rodata_start[], _
 extern char __2M_init_start[], __2M_init_end[];
 extern char __2M_rwdata_start[], __2M_rwdata_end[];
 
+bool using_2M_mapping(void);
+
 extern unsigned long xenheap_initial_phys_start;
 extern uint64_t boot_tsc_stamp;
 
--- a/xen/include/xen/efi.h
+++ b/xen/include/xen/efi.h
@@ -33,6 +33,7 @@ struct compat_pf_efi_runtime_call;
 
 bool efi_enabled(unsigned int feature);
 void efi_init_memory(void);
+bool efi_boot_mem_unused(unsigned long *start, unsigned long *end);
 bool efi_rs_using_pgtables(void);
 unsigned long efi_get_time(void);
 void efi_halt_system(void);