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Commit 1457d8cf authored by Juergen Gross's avatar Juergen Gross
Browse files

x86/xen: fix pv boot 



Commit 9da3f2b7 ("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kernel pages is no longer valid.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: 9da3f2b7 ("x86/fault: BUG() when uaccess helpers fault on kernel addresses")
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarAndrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent 6cc4a086

arch/x86/include/asm/xen/page.h

+31 −4
Original line number Diff line number Diff line
@@ -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

arch/x86/xen/p2m.c

+1 −2
Original line number Diff line number Diff line
@@ -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;