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Fri, 21 Jun 2024 16:48:10 +0000 (GMT) Received: from nasanex01b.na.qualcomm.com (nasanex01b.na.qualcomm.com [10.46.141.250]) by NASANPPMTA03.qualcomm.com (8.17.1.19/8.17.1.19) with ESMTPS id 45LGm8w3005843 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 21 Jun 2024 16:48:08 GMT Received: from hu-eberman-lv.qualcomm.com (10.49.16.6) by nasanex01b.na.qualcomm.com (10.46.141.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.9; Fri, 21 Jun 2024 09:48:07 -0700 Date: Fri, 21 Jun 2024 09:48:06 -0700 From: Elliot Berman To: Quentin Perret CC: David Hildenbrand , Jason Gunthorpe , Fuad Tabba , Christoph Hellwig , John Hubbard , Andrew Morton , Shuah Khan , Matthew Wilcox , , , , , , , Subject: Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning Message-ID: <20240621093120954-0700.eberman@hu-eberman-lv.qualcomm.com> References: <20240620135540.GG2494510@nvidia.com> <6d7b180a-9f80-43a4-a4cc-fd79a45d7571@redhat.com> <20240620142956.GI2494510@nvidia.com> <20240620140516768-0700.eberman@hu-eberman-lv.qualcomm.com> <20240620231814.GO2494510@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-Originating-IP: [10.49.16.6] X-ClientProxiedBy: nalasex01a.na.qualcomm.com (10.47.209.196) To nasanex01b.na.qualcomm.com (10.46.141.250) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: _kjYZRfv7U_QpYslJuL5ZSJCgoCZ6bnT X-Proofpoint-GUID: _kjYZRfv7U_QpYslJuL5ZSJCgoCZ6bnT X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-06-21_08,2024-06-21_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 clxscore=1015 bulkscore=0 lowpriorityscore=0 malwarescore=0 adultscore=0 mlxscore=0 priorityscore=1501 spamscore=0 impostorscore=0 phishscore=0 mlxlogscore=371 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2406140001 definitions=main-2406210121 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D4BF620008 X-Stat-Signature: thhhemd4qb5rqt4t3hu655ntq64jzgwe X-Rspam-User: X-HE-Tag: 1718988499-299869 X-HE-Meta: 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 WgmNMaG4 XlfcKTP9j/OD7gRppdOaplW1XtkQEGkZrPfoq7CjEygrPo2ZPovRMvEA565E4tsAUgaw0ZUZGH4OoEflaNxNdvmLMPWn9l/8H0LMn84lUJVuI9UfQKfGovLsXu9vzB0gF+jQldBJ0GViLyofAR/lx5RDuZQ9r0Vae4nFUWTmwLC9PFMh7OeS2A8FMzV6k0qUXsBlpNKFmwUbblmN/HYVs7Mq0um22X5XQGD2dP4zdVQcJ5Ik= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 21, 2024 at 09:25:10AM +0000, Quentin Perret wrote: > On Friday 21 Jun 2024 at 10:02:08 (+0200), David Hildenbrand wrote: > > Sure, there might be cases like "pKVM can handle access to private pages in > > user page mappings", "AMD-SNP will not crash the host if writing to private > > pages" but there are not factors that really make a difference for a common > > solution. > > Sure, there isn't much value in differentiating on these things. One > might argue that we could save one mmap() on the private->shared > conversion path by keeping all of guest_memfd mapped in userspace > including private memory, but that's most probably not worth the > effort of re-designing the whole thing just for that, so let's forget > that. > > The ability to handle stage-2 faults in the kernel has implications in > other places however. It means we don't need to punch holes in the > kernel linear map when donating memory to a guest for example, even with > 'crazy' access patterns like load_unaligned_zeropad(). So that's good. > The ability to handle stage-2 faults in the kernel is something that's specific to arm64 pKVM though. We do want to punch holes in the linear map for Gunyah case. I don't think this is blocking issue. I only want to point out we can't totally ignore the linear map. Thanks, Elliot