[Xen-devel] [PATCH] iommu: fix unused percpu in xen_in_range()

[Qing He <qing.he@xxxxxxxxx>]

On Fri, 2009-04-24 at 15:16 +0800, Keir Fraser wrote:
> On 24/04/2009 08:04, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
> 
> > Also, after suggesting to use gb-pages when possible here I realized that
> > it's probably a latent bug to map more space than was allocated - if the
> > non-allocated-but-mapped pages happen to later get allocated to a domain,
> > that domain may change the cacheability attributes of any of these pages,
> > resulting in aliasing issues. I'll put together a patch for this, but it'll 
> > be
> > a couple of days until I'll be able to do so.
> 
> I think we should shatter the superpage on demand. This would also be
> required for superpage mappings of Xen itself: when we free initmem that
> memory can now be allocated to a domain (now xenheap and domheap are merged
> on x86/64).
> 
> An alternative might be to mark such partially-freed superpages as
> Xenheap-only, and allocate them preferentially for Xenheap callers (i.e.,
> alloc those pages first, then from the general heap).
> 

Here is the patch I mentioned above, it can fix dom0 booting on my box:
---

unused percpu area is reclaimed as xenheap, but since xenheap and
domheap are shared on x86_64, it's possible dom0 can get these pages and
perform DMA on them. This patch removes this area in xen_in_range(),
so iommu 1:1 mapping for this area can be added.

Signed-off-by: Qing He <qing.he@xxxxxxxxx>

---
diff -r 8b152638adaa xen/arch/x86/setup.c
--- a/xen/arch/x86/setup.c      Thu Apr 23 16:22:48 2009 +0100
+++ b/xen/arch/x86/setup.c      Fri Apr 24 15:24:18 2009 +0800
@@ -98,6 +98,7 @@ cpumask_t cpu_present_map;
 
 unsigned long xen_phys_start;
 unsigned long allocator_bitmap_end;
+unsigned long per_cpu_used_end;
 
 #ifdef CONFIG_X86_32
 /* Limits of Xen heap, used to initialise the allocator. */
@@ -223,6 +224,8 @@ static void __init percpu_init_areas(voi
                          (first_unused << PERCPU_SHIFT),
                          (NR_CPUS - first_unused) << PERCPU_SHIFT);
 #endif
+
+    per_cpu_used_end = __pa(__per_cpu_start) + (first_unused << PERCPU_SHIFT);
 }
 
 static void __init init_idle_domain(void)
@@ -1124,9 +1127,9 @@ int xen_in_range(paddr_t start, paddr_t 
     /* initialize first time */
     if ( !xen_regions[0].s )
     {
-        extern char __init_begin[], __per_cpu_start[], __per_cpu_end[],
-                    __bss_start[];
+        extern char __init_begin[], __per_cpu_start[], __bss_start[];
         extern unsigned long allocator_bitmap_end;
+        extern unsigned long per_cpu_used_end;
 
         /* S3 resume code (and other real mode trampoline code) */
         xen_regions[0].s = bootsym_phys(trampoline_start);
@@ -1136,7 +1139,7 @@ int xen_in_range(paddr_t start, paddr_t 
         xen_regions[1].e = __pa(&__init_begin);
         /* per-cpu data */
         xen_regions[2].s = __pa(&__per_cpu_start);
-        xen_regions[2].e = __pa(&__per_cpu_end);
+        xen_regions[2].e = per_cpu_used_end;
         /* bss + boot allocator bitmap */
         xen_regions[3].s = __pa(&__bss_start);
         xen_regions[3].e = allocator_bitmap_end;
diff -r 8b152638adaa xen/arch/x86/tboot.c
--- a/xen/arch/x86/tboot.c      Thu Apr 23 16:22:48 2009 +0100
+++ b/xen/arch/x86/tboot.c      Fri Apr 24 15:24:18 2009 +0800
@@ -48,6 +48,7 @@ static uint64_t sinit_base, sinit_size;
 
 extern char __init_begin[], __per_cpu_start[], __per_cpu_end[], __bss_start[];
 extern unsigned long allocator_bitmap_end;
+extern unsigned long per_cpu_used_end;
 
 #define SHA1_SIZE      20
 typedef uint8_t   sha1_hash_t[SHA1_SIZE];
@@ -310,7 +311,7 @@ void tboot_shutdown(uint32_t shutdown_ty
                                               __pa(&_stext);
         /* per-cpu data */
         g_tboot_shared->mac_regions[2].start = 
(uint64_t)__pa(&__per_cpu_start);
-        g_tboot_shared->mac_regions[2].size = __pa(&__per_cpu_end) -
+        g_tboot_shared->mac_regions[2].size = per_cpu_used_end -
                                               __pa(&__per_cpu_start);
         /* bss */
         g_tboot_shared->mac_regions[3].start = (uint64_t)__pa(&__bss_start);



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