[PATCH 4.14 157/183] KVM: PPC: Book3S HV: Fix handling of secondary HPTEG in HPT resizing code

From: Greg Kroah-Hartman
Date: Wed Apr 25 2018 - 06:53:55 EST

4.14-stable review patch. If anyone has any objections, please let me know.


From: Paul Mackerras <paulus@xxxxxxxxxx>

[ Upstream commit 05f2bb0313a2855e491dadfc8319b7da261d7074 ]

This fixes the computation of the HPTE index to use when the HPT
resizing code encounters a bolted HPTE which is stored in its
secondary HPTE group. The code inverts the HPTE group number, which
is correct, but doesn't then mask it with new_hash_mask. As a result,
new_pteg will be effectively negative, resulting in new_hptep
pointing before the new HPT, which will corrupt memory.

In addition, this removes two BUG_ON statements. The condition that
the BUG_ONs were testing -- that we have computed the hash value
incorrectly -- has never been observed in testing, and if it did
occur, would only affect the guest, not the host. Given that
BUG_ON should only be used in conditions where the kernel (i.e.
the host kernel, in this case) can't possibly continue execution,
it is not appropriate here.

Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
arch/powerpc/kvm/book3s_64_mmu_hv.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -1348,12 +1348,8 @@ static unsigned long resize_hpt_rehash_h

new_pteg = hash & new_hash_mask;
- if (vpte & HPTE_V_SECONDARY) {
- BUG_ON(~pteg != (hash & old_hash_mask));
- new_pteg = ~new_pteg;
- } else {
- BUG_ON(pteg != (hash & old_hash_mask));
- }
+ if (vpte & HPTE_V_SECONDARY)
+ new_pteg = ~hash & new_hash_mask;

new_idx = new_pteg * HPTES_PER_GROUP + (idx % HPTES_PER_GROUP);
new_hptep = (__be64 *)(new->virt + (new_idx << 4));