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authorPaul Mackerras <paulus@ozlabs.org>2016-11-16 05:43:28 (GMT)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-01-09 07:32:22 (GMT)
commit94107133ae811e0175803639ae7ab2411e6cdb3c (patch)
tree727e97adfff6fe5f6312877386af229f67cc1855
parent75b1053c2b8c01baedf85f17be8455dadc63a383 (diff)
downloadlinux-94107133ae811e0175803639ae7ab2411e6cdb3c.tar.xz
KVM: PPC: Book3S HV: Don't lose hardware R/C bit updates in H_PROTECT
commit f064a0de1579fabded8990bed93971e30deb9ecb upstream. The hashed page table MMU in POWER processors can update the R (reference) and C (change) bits in a HPTE at any time until the HPTE has been invalidated and the TLB invalidation sequence has completed. In kvmppc_h_protect, which implements the H_PROTECT hypercall, we read the HPTE, modify the second doubleword, invalidate the HPTE in memory, do the TLB invalidation sequence, and then write the modified value of the second doubleword back to memory. In doing so we could overwrite an R/C bit update done by hardware between when we read the HPTE and when the TLB invalidation completed. To fix this we re-read the second doubleword after the TLB invalidation and OR in the (possibly) new values of R and C. We can use an OR since hardware only ever sets R and C, never clears them. This race was found by code inspection. In principle this bug could cause occasional guest memory corruption under host memory pressure. Fixes: a8606e20e41a ("KVM: PPC: Handle some PAPR hcalls in the kernel", 2011-06-29) Signed-off-by: Paul Mackerras <paulus@ozlabs.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/powerpc/kvm/book3s_hv_rm_mmu.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 99b4e9d..5420d06 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -653,6 +653,8 @@ long kvmppc_h_protect(struct kvm_vcpu *vcpu, unsigned long flags,
HPTE_V_ABSENT);
do_tlbies(kvm, &rb, 1, global_invalidates(kvm, flags),
true);
+ /* Don't lose R/C bit updates done by hardware */
+ r |= be64_to_cpu(hpte[1]) & (HPTE_R_R | HPTE_R_C);
hpte[1] = cpu_to_be64(r);
}
}