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x86/xen: fix pv boot

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Commit 9da3f2b740 ("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kernel pages is no longer valid.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: 9da3f2b740 ("x86/fault: BUG() when uaccess helpers fault on kernel addresses")
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2018-11-07 18:01:00 +01:00
parent 6cc4a0863c
commit 1457d8cf76
2 changed files with 32 additions and 6 deletions
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35
arch/x86/include/asm/xen/page.h
View file

@ -9,7 +9,7 @@
#include <linux/mm.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <asm/extable.h>
#include <asm/page.h>
#include <asm/pgtable.h>
@ -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

3
arch/x86/xen/p2m.c
View file

@ -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;