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[34.124.129.10]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82b0409c0f1sm1652552b3a.38.2026.03.20.02.28.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Mar 2026 02:28:36 -0700 (PDT) Date: Fri, 20 Mar 2026 09:28:28 +0000 From: Pranjal Shrivastava To: Vipin Sharma Cc: Samiullah Khawaja , David Woodhouse , Lu Baolu , Joerg Roedel , Will Deacon , Jason Gunthorpe , Robin Murphy , Kevin Tian , Alex Williamson , Shuah Khan , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Saeed Mahameed , Adithya Jayachandran , Parav Pandit , Leon Romanovsky , William Tu , Pratyush Yadav , Pasha Tatashin , David Matlack , Andrew Morton , Chris Li , YiFei Zhu Subject: Re: [PATCH 04/14] iommu/pages: Add APIs to preserve/unpreserve/restore iommu pages Message-ID: References: <20260203220948.2176157-1-skhawaja@google.com> <20260203220948.2176157-5-skhawaja@google.com> <20260317202925.GA2582517.vipinsh@google.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: <20260317202925.GA2582517.vipinsh@google.com> On Tue, Mar 17, 2026 at 01:59:03PM -0700, Vipin Sharma wrote: > On Tue, Feb 03, 2026 at 10:09:38PM +0000, Samiullah Khawaja wrote: > > + > > +void iommu_unpreserve_pages(struct iommu_pages_list *list, int count) > > +{ > > + struct ioptdesc *iopt; > > + > > + if (!count) > > + return; > > + > > + /* If less than zero then unpreserve all pages. */ > > + if (count < 0) > > + count = 0; > > + > > + list_for_each_entry(iopt, &list->pages, iopt_freelist_elm) { > > + kho_unpreserve_folio(ioptdesc_folio(iopt)); > > + if (count > 0 && --count == 0) > > + break; > > + } > > +} > > I see you are trying to have common function for error handling in > iommu_preserve_pages() down and unpreserving in the next patch with > overloaded meaning of count. > > < 0 means unpreserve all of the pages > = 0 means do nothing > > 0 unpreserve these many pages. > > It seems non-intuitive to me and code also end up having multiple ifs. I > will recommend to just have this function go through all of the pages > without passing count argument. In iommu_preserve_pages() function down, > handle the error case with a "goto err" statement. If this is the way > things happen in iommu codebase feel free to ignore this suggestion. > +1 to this. The current version of overloaded count is counter-intuitive as it expects a back-handed API contract. Since we're using lists here, I'd recommend using the list_for_each_entry_continue_reverse() helper: +void iommu_unpreserve_pages(struct iommu_pages_list *list) +{ + struct ioptdesc *iopt; + + list_for_each_entry(iopt, &list->pages, iopt_freelist_elm) + kho_unpreserve_folio(ioptdesc_folio(iopt)); +} +EXPORT_SYMBOL_GPL(iommu_unpreserve_pages); + +int iommu_preserve_pages(struct iommu_pages_list *list) +{ + struct ioptdesc *iopt; + int ret; + + list_for_each_entry(iopt, &list->pages, iopt_freelist_elm) { + ret = kho_preserve_folio(ioptdesc_folio(iopt)); + if (ret) + goto err_rollback; + } + return 0; + +err_rollback: + /* Rollback only the successfully preserved pages */ + list_for_each_entry_continue_reverse(iopt, &list->pages, iopt_freelist_elm) + kho_unpreserve_folio(ioptdesc_folio(iopt)); + return ret; +} [ ---- snip >8---- ] Thanks, Praan