diff options
Diffstat (limited to '0049-x86-shadow-fix-and-improve-sh_page_has_multiple_shad.patch')
| -rw-r--r-- | 0049-x86-shadow-fix-and-improve-sh_page_has_multiple_shad.patch | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/0049-x86-shadow-fix-and-improve-sh_page_has_multiple_shad.patch b/0049-x86-shadow-fix-and-improve-sh_page_has_multiple_shad.patch new file mode 100644 index 0000000..0abf7e9 --- /dev/null +++ b/0049-x86-shadow-fix-and-improve-sh_page_has_multiple_shad.patch @@ -0,0 +1,47 @@ +From cab866ee62d860e9ff4abe701163972d4e9f896d Mon Sep 17 00:00:00 2001 +From: Jan Beulich <jbeulich@suse.com> +Date: Fri, 31 Mar 2023 08:38:42 +0200 +Subject: [PATCH 49/61] x86/shadow: fix and improve + sh_page_has_multiple_shadows() + +While no caller currently invokes the function without first making sure +there is at least one shadow [1], we'd better eliminate UB here: +find_first_set_bit() requires input to be non-zero to return a well- +defined result. + +Further, using find_first_set_bit() isn't very efficient in the first +place for the intended purpose. + +Signed-off-by: Jan Beulich <jbeulich@suse.com> +Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> + +[1] The function has exactly two uses, and both are from OOS code, which + is HVM-only. For HVM (but not for PV) sh_mfn_is_a_page_table(), + guarding the call to sh_unsync(), guarantees at least one shadow. + Hence even if sh_page_has_multiple_shadows() returned a bogus value + when invoked for a PV domain, the subsequent is_hvm_vcpu() and + oos_active checks (the former being redundant with the latter) will + compensate. (Arguably that oos_active check should come first, for + both clarity and efficiency reasons.) +master commit: 2896224a4e294652c33f487b603d20bd30955f21 +master date: 2023-03-24 11:07:08 +0100 +--- + xen/arch/x86/mm/shadow/private.h | 2 +- + 1 file changed, 1 insertion(+), 1 deletion(-) + +diff --git a/xen/arch/x86/mm/shadow/private.h b/xen/arch/x86/mm/shadow/private.h +index 738214f75e..762214f73c 100644 +--- a/xen/arch/x86/mm/shadow/private.h ++++ b/xen/arch/x86/mm/shadow/private.h +@@ -324,7 +324,7 @@ static inline int sh_page_has_multiple_shadows(struct page_info *pg) + return 0; + shadows = pg->shadow_flags & SHF_page_type_mask; + /* More than one type bit set in shadow-flags? */ +- return ( (shadows & ~(1UL << find_first_set_bit(shadows))) != 0 ); ++ return shadows && (shadows & (shadows - 1)); + } + + #if (SHADOW_OPTIMIZATIONS & SHOPT_OUT_OF_SYNC) +-- +2.40.0 + |