Balbir Singh <bsingharora@xxxxxxxxx> writes: > Some KVM functions for book3s_hv are called in real mode. > In real mode the top 4 bits of the address space are ignored, > hence an address beginning with 0xc0000000+offset is the > same as 0xd0000000+offset. The issue was observed when > a kvm memslot resolution lead to random values when > access from kvmppc_h_enter(). The issue is hit if the > KVM host is running with a page size of 4K, since > kvzalloc() looks at size < PAGE_SIZE. On systems with > 64K the issue is not observed easily, it largely depends > on the size of the structure being allocated. > > The proposed fix moves all KVM allocations for book3s_hv > to kzalloc() until all structures used in real mode are > audited. For safety allocations are moved to kmalloc > space. The impact is a large allocation on systems with > 4K page size. We did such access using *real_vmalloc_addr(void *x). So you are suggesting here is we don't do that for all code path ? Do you have a stack dump for which you identified the issue ? > > Signed-off-by: Balbir Singh <bsingharora@xxxxxxxxx> > --- > Changelog v2: > Fix build failures reported by the kbuild test robot > http://www.spinics.net/lists/kvm/msg141727.html > > arch/powerpc/include/asm/kvm_host.h | 19 +++++++++++++++++++ > include/linux/kvm_host.h | 11 +++++++++++ > virt/kvm/kvm_main.c | 2 +- > 3 files changed, 31 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h > index f15713a..53f5172 100644 > --- a/arch/powerpc/include/asm/kvm_host.h > +++ b/arch/powerpc/include/asm/kvm_host.h > @@ -734,6 +734,25 @@ struct kvm_vcpu_arch { > #define __KVM_HAVE_ARCH_WQP > #define __KVM_HAVE_CREATE_DEVICE > > +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE > +#define __KVM_HAVE_ARCH_VZALLOC_OVERRIDE do we need that OVERRIDE ? We usually have HAVE_ARCH_KVM_VZALLOC or just say #ifndef kvm_arch_vzalloc ? > + > +/* > + * KVM uses some of these data structures -- the ones > + * from kvzalloc() in real mode. If the data structure > + * happens to come from a vmalloc'd range then its access > + * in real mode will lead to problems due to the aliasing > + * issue - (top 4 bits are ignore). > + * A 0xd000+offset will point to a 0xc000+offset in realmode > + * Hence we want our data structures from come from kmalloc'd > + * regions, so that we don't have these aliasing issues > + */ > +static inline void *kvm_arch_vzalloc(unsigned long size) > +{ > + return kzalloc(size, GFP_KERNEL); > +} > +#endif .... -aneesh -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
