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Mon, 20 Jul 2026 09:56:37 +0000 (GMT) Received: from [9.111.21.55] (unknown [9.111.21.55]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 20 Jul 2026 09:56:37 +0000 (GMT) Message-ID: <30f0084c-5621-4602-8c0a-9082dd9d3d43@linux.ibm.com> Date: Mon, 20 Jul 2026 11:56:36 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/8] KVM: s390: pv: Use VM_SPARSE area for guest variable storage area To: Heiko Carstens , Alexander Gordeev , Sven Schnelle , Vasily Gorbik , Janosch Frank , Claudio Imbrenda , David Hildenbrand Cc: linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260720085834.898025-1-hca@linux.ibm.com> <20260720085834.898025-2-hca@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20260720085834.898025-2-hca@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=HJXz0Itv c=1 sm=1 tr=0 ts=6a5df0da cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=YKi7x7nYPf8b3Ghbl54A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzIwMDEwOCBTYWx0ZWRfX8SPdGrCuxMK/ 9+FgjwTdAhWlCUrJS3zEV1tls5NJDb5DxVgGgtGyS5R+wjW+/HnbyyYJJ3fVbknPlf9FKHj03oL /CnaEYCN+FwrZnv8dSlzM/Ct/GbnzyNfQVABMAzHVR+l3rbsaPM2QSPkyPvaYvh4Ggdag/R3inN +FPzcaeuBIC05h2gguT84buC92LZRzdYrM+M8W/PRcBwZK1OaBoAhOSDzS4UVtGQYBTjcXFrQGu aXAssaImxp05QPZ4RmsDw4uF+FI6F3nqFPkHjaK6X+m5KlUAC/wf9zD+hvFsRx3rJH7HX/jtgkU F5QEUmyom0qYOeS1aAzUhRw5viCqVWSwQ1oCwY8c/h8Vza9tsq0G7qTgRr+W2mY260TsWGtPEDY S06Kh+TokPYqAFs94yoTe3rzVkr+kcespPm0xlJf/Ac9Q7JP11PdCNGsJeOyuaVgQ7905NhrCx6 j7C4NVwX4fGzwembavA== X-Proofpoint-ORIG-GUID: AlkHTrDAcqJ_ZXHfjLA6-ONkhq-ZPbUs X-Proofpoint-Spam-Info: AW1haW4tMjYwNzIwMDEwOCBTYWx0ZWRfXyMJu2fuBk09/ z/P9yTWGsYuAUyTXLPOnemS++wWTDTVOQpi8NBN08nVvSNAWwNFQnOLek3gukNcwm+wt6qyAItG hCtQ+kXgniB6afhk9IRu5WLOyw5Ur6E= X-Proofpoint-GUID: AlkHTrDAcqJ_ZXHfjLA6-ONkhq-ZPbUs X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-20_01,2026-07-17_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 suspectscore=0 malwarescore=0 impostorscore=0 clxscore=1015 phishscore=0 spamscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607200108 Am 20.07.26 um 10:58 schrieb Heiko Carstens: > The guest variable storage area is allocated with vmalloc and then > donated to the ultravisor. Any kernel access to that area will result > in a secure storage access exception (aka fault). > > This is a problem if such a memory area is read via /proc/kcore. This > causes an exception via vread_iter() and results in an unexpected short > read. Avoid this by allocating a custom VM_SPARSE area. If such an area > is read, vread_iter() returns zeroes for the entire area. > > Note that the function which frees the area does not update ptes. This > is intentional to allow for deferred / lazy pte updates and TLB flushing > like the generic vfree() code is doing that. See vunmap_pte_range(). > > This assumes that s390 will gain full support for lazy_mmu_mode_enable() > and lazy_mmu_mode_disable() in the future, since as of now the used > ptep_get_and_clear() in vunmap_pte_range() does indeed invalidate and > flush every single pte entry, but only for s390. > > Tested-by: Christian Borntraeger > Signed-off-by: Heiko Carstens Reviewed-by: Christian Borntraeger [..]> +static int uv_free_range_cb(pte_t *ptep, unsigned long addr, void *data) > +{ > + pte_t pte = ptep_get(ptep); > + > + if (!pte_present(pte)) > + return 0; I guess we do not need it today, but it certainly does not hurt?