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Wed, 18 Mar 2026 21:45:25 +0000 (GMT) Message-ID: Date: Wed, 18 Mar 2026 22:45:24 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 6/7] KVM: s390: vsie: Fix off-by-one when protecting guest page tables To: Claudio Imbrenda , kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, nsg@linux.ibm.com, nrb@linux.ibm.com, seiden@linux.ibm.com, gra@linux.ibm.com, schlameuss@linux.ibm.com, hca@linux.ibm.com, david@kernel.org References: <20260318140853.119460-1-imbrenda@linux.ibm.com> <20260318140853.119460-7-imbrenda@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20260318140853.119460-7-imbrenda@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=arO/yCZV c=1 sm=1 tr=0 ts=69bb1cfa cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=SmNStjwj_dqeLPw4z3EA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE4MDE4OCBTYWx0ZWRfXx5KGBRgUMEzO +wedoQ04Mo0SxbmFZ2IRdkSBHgucM+B94beyMJ/v32YmjFQK0Om8aW9bZth6dQiLc6WI4GCX22p 75SewUyCBf5ZrJ8IhuApMnLN28dB+uB3zcrurbhQx4YyRknVyN0bJPZdyzigJOA/VclHkV7QAhY eOdzWwtRGnd+YZKK4uZDREtrK6eh3LznF/le0G1W4h5KF6JhITTPJi70OHZJEKlzXOhI4xeIS+X N9XXzDDy8e+kl08jmqvf36ZNN/5i1nl8vpevo2b7f3W9iyx4iSH5HipCgpCQX88mxfsBbZSA1lE 9E6pBbQZ3vxzpFrGcrWReIi5PpCuq/gnuGkoyTNXCjHtM2P+farjRHkScKM34H9vZbKendU/UXa 1ggW1gjZLvNr5puKSqq+JcTl/VjnqUFtNnaEn9jV+bRJHzWFTN1O+RiXETGeyv0PIO4YACaurmJ D1PHFCQ/+IkGsdg6TrA== X-Proofpoint-GUID: tQxE0om5C5JHEAtRYYZBeia3x7fL69vx X-Proofpoint-ORIG-GUID: tQxE0om5C5JHEAtRYYZBeia3x7fL69vx X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-18_01,2026-03-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 lowpriorityscore=0 impostorscore=0 adultscore=0 bulkscore=0 suspectscore=0 malwarescore=0 clxscore=1015 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603180188 Am 18.03.26 um 15:08 schrieb Claudio Imbrenda: > When shadowing, the guest page tables are write-protected, in order to > trap changes and properly unshadow the shadow mapping for the nested > guest. Already shadowed levels are skipped, so that only the needed > levels are write protected. > > Currently the levels that get write protected are exactly one level too > deep: the last level (nested guest memory) gets protected in the wrong > way, and will be protected again correctly a few lines afterwards; most > importantly, the highest non-shadowed level does *not* get write > protected. > > This leads to all sorts of races and other issues. > > Write protect the correct levels, so that all the levels that need to > be protected are protected, and avoid double protecting the last level. > > Signed-off-by: Claudio Imbrenda > Fixes: e38c884df921 ("KVM: s390: Switch to new gmap") Tested-by: Christian Borntraeger > --- > arch/s390/kvm/gaccess.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c > index 3bcf988d6faa..8b287fcf611d 100644 > --- a/arch/s390/kvm/gaccess.c > +++ b/arch/s390/kvm/gaccess.c > @@ -1516,8 +1516,8 @@ static int _gaccess_do_shadow(struct kvm_s390_mmu_cache *mc, struct gmap *sg, > * only the page containing the entry, not the whole table. > */ > for (i = gl ; i >= w->level; i--) { > - rc = gmap_protect_rmap(mc, sg, entries[i - 1].gfn, gpa_to_gfn(saddr), > - entries[i - 1].pfn, i, entries[i - 1].writable); > + rc = gmap_protect_rmap(mc, sg, entries[i].gfn, gpa_to_gfn(saddr), > + entries[i].pfn, i + 1, entries[i].writable); > if (rc) > return rc; > if (!sg->parent)