linux-kernel - Re: [PATCH RFC 1/2] s390x: mm: allow mixed page table types (2k and 4k)

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Message-Id: <2a3d5383-cab4-6882-4050-c69404bda347@de.ibm.com>
Date:   Thu, 1 Jun 2017 13:39:37 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Thomas Huth <thuth@...hat.com>
Subject: Re: [PATCH RFC 1/2] s390x: mm: allow mixed page table types (2k and
 4k)

On 05/29/2017 06:32 PM, David Hildenbrand wrote:

>  	new = old = pgste_get_lock(ptep);
>  	pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT |
> @@ -748,6 +764,11 @@ int reset_guest_reference_bit(struct mm_struct *mm, unsigned long addr)
>  	ptep = get_locked_pte(mm, addr, &ptl);
>  	if (unlikely(!ptep))
>  		return -EFAULT;
> +	if (!pgtable_has_pgste(mm, __pa(ptep))) {
> +		pte_unmap_unlock(ptep, ptl);
> +		WARN_ONCE(true, "Guest address on page table without pgste");

All these WARN_ONCE. Is there a way how a malicious user can trigger this or is this checked
everywhere and triggered would be indeed a bug?