Re: [PATCH] KVM: arm/arm64: add WARN_ON if size is not PAGE_SIZE aligned in unmap_stage2_range

[Suzuki K Poulose]

Hi Jia,

On 17/05/18 07:11, Jia He wrote:
> I ever met a panic under memory pressure tests(start 20 guests and run
> memhog in the host).

Please avoid using "I" in the commit description and preferably stick to
an objective description.

> The root cause might be what I fixed at [1]. But from arm kvm points of
> view, it would be better we caught the exception earlier and clearer.
>
> If the size is not PAGE_SIZE aligned, unmap_stage2_range might unmap the
> wrong(more or less) page range. Hence it caused the "BUG: Bad page
> state"

I don't see why we should ever panic with a "positive" size value. Anyways,
the unmap requests must be in units of pages. So this check might be useful.


Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

> [1] https://lkml.org/lkml/2018/5/3/1042
>
> Signed-off-by: jia.he@xxxxxxxxxxxxxxxx
> ---
>   virt/kvm/arm/mmu.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 7f6a944..8dac311 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -297,6 +297,8 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size)
>   	phys_addr_t next;
>   
>   	assert_spin_locked(&kvm->mmu_lock);
> +	WARN_ON(size & ~PAGE_MASK);
> +
>   	pgd = kvm->arch.pgd + stage2_pgd_index(addr);
>   	do {
>   		/*