Commit 9da3f2b7405440 ("x86/fault: BUG() when uaccess helpers fault on
kernel addresses") introduced a regression for booting Xen PV guests.
Xen PV guests are using __put_user() and __get_user() for accessing the
p2m map (physical to machine frame number map) as accesses might fail
in case of not populated areas of the map.
With above commit using __put_user() and __get_user() for accessing
kernel pages is no longer valid. So replace the Xen hack by adding
appropriate p2m access functions using the default fixup handler.
Fixes: 9da3f2b7405440 ("x86/fault: BUG() when uaccess helpers fault on kernel
addresses")
Signed-off-by: Juergen Gross
---
arch/x86/include/asm/xen/page.h | 35 +++
arch/x86/xen/p2m.c | 3 +--
2 files changed, 32 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index 123e669bf363..790ce08e41f2 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -9,7 +9,7 @@
#include
#include
-#include
+#include
#include
#include
@@ -93,12 +93,39 @@ clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref
*unmap_ops,
*/
static inline int xen_safe_write_ulong(unsigned long *addr, unsigned long val)
{
- return __put_user(val, (unsigned long __user *)addr);
+ int ret = 0;
+
+ asm volatile("1: mov %[val], %[ptr]\n"
+"2:\n"
+".section .fixup, \"ax\"\n"
+"3: sub $1, %[ret]\n"
+" jmp 2b\n"
+".previous\n"
+_ASM_EXTABLE(1b, 3b)
+: [ret] "+r" (ret), [ptr] "=m" (*addr)
+: [val] "r" (val));
+
+ return ret;
}
-static inline int xen_safe_read_ulong(unsigned long *addr, unsigned long *val)
+static inline int xen_safe_read_ulong(const unsigned long *addr,
+ unsigned long *val)
{
- return __get_user(*val, (unsigned long __user *)addr);
+ int ret = 0;
+ unsigned long rval = ~0ul;
+
+ asm volatile("1: mov %[ptr], %[rval]\n"
+"2:\n"
+".section .fixup, \"ax\"\n"
+"3: sub $1, %[ret]\n"
+" jmp 2b\n"
+".previous\n"
+_ASM_EXTABLE(1b, 3b)
+: [ret] "+r" (ret), [rval] "+r" (rval)
+: [ptr] "m" (*addr));
+ *val = rval;
+
+ return ret;
}
#ifdef CONFIG_XEN_PV
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index b06731705529..055e37e43541 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -656,8 +656,7 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long
mfn)
/*
* The interface requires atomic updates on p2m elements.
-* xen_safe_write_ulong() is using __put_user which does an atomic
-* store via asm().
+* xen_safe_write_ulong() is using an atomic store via asm().
*/
if (likely(!xen_safe_write_ulong(xen_p2m_addr + pfn, mfn)))
return true;
--
2.16.4
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