On Wed, Feb 07, 2018 at 08:04:45PM +1100, Paul Mackerras wrote:
> 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.
Fair enough. I think those were there because they were useful during
early development, but should have been removed after that.
>
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> ---
> 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 9660972..d196499 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -1329,12 +1329,8 @@ 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));
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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