Messages in this thread | | | Date | Fri, 22 May 2015 20:42:31 -0400 | From | Boris Ostrovsky <> | Subject | Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization |
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On 05/22/2015 07:54 PM, Bandan Das wrote: > Boris Ostrovsky <boris.ostrovsky@oracle.com> writes: > >> On 05/11/2015 10:55 AM, Xiao Guangrong wrote: >>> KVM may turn a user page to a kernel page when kernel writes a readonly >>> user page if CR0.WP = 1. This shadow page entry will be reused after >>> SMAP is enabled so that kernel is allowed to access this user page >>> >>> Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu >>> once CR4.SMAP is updated >>> >>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com> >>> --- >> >> >>> >>> @@ -4208,12 +4211,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa, >>> const u8 *new, int bytes) >>> { >>> gfn_t gfn = gpa >> PAGE_SHIFT; >>> - union kvm_mmu_page_role mask = { .word = 0 }; >>> struct kvm_mmu_page *sp; >>> LIST_HEAD(invalid_list); >>> u64 entry, gentry, *spte; >>> int npte; >>> bool remote_flush, local_flush, zap_page; >>> + union kvm_mmu_page_role mask = (union kvm_mmu_page_role) { >>> + .cr0_wp = 1, >>> + .cr4_pae = 1, >>> + .nxe = 1, >>> + .smep_andnot_wp = 1, >>> + .smap_andnot_wp = 1, >>> + }; >>> >>> >> >> >> This breaks older compilers that can't initialize anon structures. > > How old ? Even gcc 3.1 says you can use unnamed struct/union fields and > 3.2 is the minimum version required to compile the kernel as mentioned > in the README. > > We could simply just name the structure, but I doubt this is the > only place in the kernel code where it's being used this way :)
You can use them but you can't use initializers. Unfortunately my build system (F13) conveniently went down but this is an example from an old email:
FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap> cat anon.c struct bar { struct { int i; }; };
main() { struct bar a = {.i = 0}; }
FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap> gcc --version|head -1 gcc (GCC) 4.4.4 20100503 (Red Hat 4.4.4-2) FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap> gcc anon.c anon.c: In function ‘main’: anon.c:9: error: unknown field ‘i’ specified in initializer FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap>
but
build@build-mk2 bootstrap]$ gcc --version|head -1 gcc (GCC) 4.6.3 20120306 (Red Hat 4.6.3-2) [build@build-mk2 bootstrap]$ gcc anon.c [build@build-mk2 bootstrap]$
-boris
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