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[34.83.46.153]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84149619c9dsm224416b3a.36.2026.05.20.12.50.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 May 2026 12:50:43 -0700 (PDT) Date: Wed, 20 May 2026 19:50:40 +0000 From: Samiullah Khawaja To: Pranjal Shrivastava Cc: David Woodhouse , Lu Baolu , Joerg Roedel , Will Deacon , Jason Gunthorpe , YiFei Zhu , 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 , Vipin Sharma Subject: Re: [PATCH v2 12/16] iommufd: Implement ioctl to mark HWPT for preservation Message-ID: References: <20260427175633.1978233-1-skhawaja@google.com> <20260427175633.1978233-13-skhawaja@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; format=flowed Content-Disposition: inline In-Reply-To: On Tue, May 19, 2026 at 11:05:02PM +0000, Pranjal Shrivastava wrote: >On Mon, Apr 27, 2026 at 05:56:29PM +0000, Samiullah Khawaja wrote: >> From: YiFei Zhu >> >> Userspace provides a token to mark the HWPT for preservation. Note that >> this token is not the LUO token that is used to preserve the iommufd. >> Once all the required HWPT are marked for preservation, the user can >> preserve the iommufd into LUO. The iommufd will preserve the HWPTs that >> are marked for preservation. >> >> The marked HWPTs are tracked using a new XArray mark protected by a new >> liveupdate mutex. This mutex will also be used during iommufd >> preservation to protect against any race with the mark preserve ioctl. >> >> The HWPT token will be used during restore to identify this HWPT. The >> restoration logic is not implemented and will be added later. >> >> Signed-off-by: YiFei Zhu >> Signed-off-by: Samiullah Khawaja > [snip] > >> +int iommufd_hwpt_liveupdate_mark_preserve(struct iommufd_ucmd *ucmd) >> +{ >> + struct iommu_hwpt_liveupdate_mark_preserve *cmd = ucmd->cmd; >> + struct iommufd_hwpt_paging *hwpt_target; >> + struct iommufd_hwpt_paging *hwpt_paging; >> + struct iommufd_ctx *ictx = ucmd->ictx; >> + struct iommufd_object *obj; >> + unsigned long index; >> + int rc = 0; >> + >> + hwpt_target = iommufd_get_hwpt_paging(ucmd, cmd->hwpt_id); >> + if (IS_ERR(hwpt_target)) >> + return PTR_ERR(hwpt_target); >> + >> + mutex_lock(&ictx->liveupdate_mutex); >> + >> + xa_lock(&ictx->objects); >> + xa_for_each_marked(&ictx->objects, index, obj, IOMMUFD_OBJ_LIVEUPDATE_MARK) { >> + if (WARN_ON_ONCE(obj->type != IOMMUFD_OBJ_HWPT_PAGING)) >> + continue; >> + >> + hwpt_paging = to_hwpt_paging(container_of(obj, struct iommufd_hw_pagetable, obj)); >> + if (hwpt_paging->liveupdate_token == cmd->hwpt_token) { >> + rc = -EADDRINUSE; >> + goto out_unlock; >> + } >> + } >> + > >Nit: What happens if the user calls this IOCTL on an HWPT that is already >marked but passes a different token? > >The xa_for_each_marked loop will not match the new token (so it bypasses >-EADDRINUSE case) and the code will silently overwrite the HWPT's >existing token? > >Since there is no unmark / update UAPI, It can be a fair policy as well, >but maybe we should call it out explicitly, maybe a log like: >dev_warn("Overwriting token to %d ...") ? Agreed. I will do this. > >If NOT, then we should avoid overwriting the token and scream with >retval like -EINVAL & dev_err in dmesg. > >> + __xa_set_mark(&ictx->objects, hwpt_target->common.obj.id, IOMMUFD_OBJ_LIVEUPDATE_MARK); >> + hwpt_target->liveupdate_token = cmd->hwpt_token; >> + >> +out_unlock: >> + xa_unlock(&ictx->objects); >> + mutex_unlock(&ictx->liveupdate_mutex); >> + iommufd_put_object(ictx, &hwpt_target->common.obj); >> + return rc; >> +} > >With those two nits addressed, > >Reviewed-by: Pranjal Shrivastava > >Thanks, >Praan Thanks, Sami