linux-kernel - [PATCH AUTOSEL for 4.15 174/189] KVM: PPC: Book3S HV: Fix handling of secondary HPTEG in HPT resizing code

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Message-ID: <20180409001637.162453-174-alexander.levin@microsoft.com>
Date:   Mon, 9 Apr 2018 00:19:06 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Paul Mackerras <paulus@...abs.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.15 174/189] KVM: PPC: Book3S HV: Fix handling of
 secondary HPTEG in HPT resizing code

From: Paul Mackerras <paulus@...abs.org>

[ 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@...son.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@...abs.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 arch/powerpc/kvm/book3s_64_mmu_hv.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index b73dbc9e797d..dc0f2ade589e 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -1337,12 +1337,8 @@ static unsigned long resize_hpt_rehash_hpte(struct kvm_resize_hpt *resize,
 	}

 	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));
-- 
2.15.1