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Tue, 18 Nov 2025 15:28:16 +0000 (GMT) Date: Tue, 18 Nov 2025 16:28:15 +0100 From: Heiko Carstens To: Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, nsg@linux.ibm.com, nrb@linux.ibm.com, seiden@linux.ibm.com, schlameuss@linux.ibm.com, svens@linux.ibm.com, agordeev@linux.ibm.com, gor@linux.ibm.com, david@redhat.com, gerald.schaefer@linux.ibm.com Subject: Re: [PATCH v3 00/23] KVM: s390: gmap rewrite, the real deal Message-ID: <20251118152815.9674D33-hca@linux.ibm.com> References: <20251106161117.350395-1-imbrenda@linux.ibm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251106161117.350395-1-imbrenda@linux.ibm.com> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=C/nkCAP+ c=1 sm=1 tr=0 ts=691c9096 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=kj9zAlcOel0A:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Kl6ix_ddhmwOMEz-dRMA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-GUID: idbAXaip6qEb1IiIW-iclLQymLPOAgzU X-Proofpoint-ORIG-GUID: idbAXaip6qEb1IiIW-iclLQymLPOAgzU X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfX/wkNy21JYIcI dKkG5zoenFuFm76MIyQB02GqPqX4AbS75nyAyKYjV5CWE7hNsx9TcieWdICWCYv2PwTfM9IR2z9 QyEIg/7TG4rapRRPiH+WQaEk2uqbaDjSS3WTcKRwBbiMOnMa+ypcFQJW3+FAEA7SG5nVG1rE4vr CHTcziBquabWTAJe7thudl9gyxZpVc+ECwlwwqo3JliMYG9XfOHdzbwN9940XKxJsifeHAq9EyE 2bgH6GRkHA/oUvPQeJNL4sCzNgLwY+4yIWheTmGQRG6X09wrJQ4OPU3dMRQmmG6q7hwmLqNnoFW mr601/ycNZ2Q9KDiSlpnKj0q0pmaMxk/Qm4MgkEODwQmz6M84GypSE/3E/0AiH4abRy+4IMtSE5 aYULY03YHO8xXrT0yfSZRbr8Iv17Vg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-18_01,2025-11-18_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 spamscore=0 impostorscore=0 bulkscore=0 malwarescore=0 suspectscore=0 clxscore=1011 lowpriorityscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511150032 On Thu, Nov 06, 2025 at 05:10:54PM +0100, Claudio Imbrenda wrote: > This series is the last big series of the gmap rewrite. It introduces > the new code and actually uses it. The old code is then removed. > > The insertions/deletions balance is negative both for this series, and > for the whole rewrite, also considering all the preparatory patches. > > KVM on s390 will now use the mmu_notifier, like most other > architectures. The gmap address space is now completely separate from > userspace; no level of the page tables is shared between guest mapping > and userspace. > > One of the biggest advantages is that the page size of userspace is > completely independent of the page size used by the guest. Userspace > can mix normal pages, THPs, hugetlbfs, and more. > > Patches 1 to 6 are mostly preparations; introducing some new bits and > functions, and moving code around. > > Patch 7 to 16 is the meat of the new gmap code; page table management > functions and gmap management. This is the code that will be used to > manage guest memory. > > Patch 18 is unfortunately big; the existing code is converted to use > the new gmap and all references to the old gmap are removed. This needs > to be done all at once, unfortunately, hence the size of the patch. > > Patch 19 and 20 remove all the now unused code. > > Patch 21 and 22 allow for 1M pages to be used to back guests, and add > some more functions that are useful for testing. > > Patch 23 fixes storage key manipulation functions, which would > otherwise be broken by the new code. I would guess patch 23 also needs to go into the already huge patch which switches everything to the new gmap code, since otherwise bisect will not work for anything that is storage key related. Anyway, I can imagine some addon cleanups, but that can wait after this series is upstream. At least from a "core s390 code view", without considering kvm this looks good to me. There is at least one known bug hiding in this huge rewrite - but just wanted to let you know that my concerns with the previous version have been addressed.