From 1457d8cf7664f34c4ba534c1073821a559a2f6f9 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Wed, 7 Nov 2018 18:01:00 +0100 Subject: [PATCH] x86/xen: fix pv boot 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 With above commit using __put_user() and __get_user() for accessing kernel pages is no longer valid.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 Reviewed-by: Andrew Cooper 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 d6d74efd8912..4fe84436d5a7 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; -- 2.30.2