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Fri, 24 Jul 2026 09:46:05 -0700 (PDT) Date: Fri, 24 Jul 2026 16:46:04 +0000 From: Pasha Tatashin To: Pratyush Yadav Cc: Pasha Tatashin , Tarun Sahu , Andrew Morton , linux-mm@kvack.org, Mike Rapoport , Alexander Graf , skhawaja@google.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 3/3] luo: Update serialized data to use KHOSER_PTR Message-ID: References: <20260628001114.1869564-1-tarunsahu@google.com> <20260628001114.1869564-4-tarunsahu@google.com> <178271651966.13502.2620034351625890943.b4-review@b4> <2vxzldbklb18.fsf@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2vxzldbklb18.fsf@kernel.org> X-Rspam-User: X-Rspamd-Queue-Id: 9CFFCA0014 X-Rspamd-Server: rspam01 X-Stat-Signature: 3ttand3we8whxxw46kmqjqykncxguizc X-HE-Tag: 1784911567-449425 X-HE-Meta: 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 bmgVlDMa ekPxlIleuq32QXgjmWfNnrY42QbVoTv+9PxqyYlCLFSIfipY8O6CHZo5d8JC/MmBFUsJHLi1xI9zlCm7X7wWA4zDO1npvFeBjKFIHW3Q8CvDHG/uooNP4ZKu4m9UVJYy0nmLu++hJ+x9A3IpfIMvE2Hb225xl86FSK4/KS7/INqIPiPiGiQKIvvM8HE5xUJIeEKp+fZNvGkjHJIa+s9ccbtfSi72uv7ph0+/5khEpTKoqXLOeyDk9cSmPG70xkGanwghYSY77a1/MNxsOLbKpJRomqB4TnfEKklB8+8g+RK2bbZPt9wnrDCgEocIMP7m8T4W3eU98R2slBVvmf4ol+HJZPcpLLXkL+z8eiM7B7COWPRiur4WfJVbJQjyi/rnvygNJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 07-09 12:20, Pratyush Yadav wrote: > Hi Pasha, > > On Mon, Jun 29 2026, Pasha Tatashin wrote: > > > On Sun, 28 Jun 2026 00:11:14 +0000, Tarun Sahu wrote: > >> diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h > >> index 288076de6d4a..9e78625cfdc1 100644 > >> --- a/include/linux/kho/abi/luo.h > >> +++ b/include/linux/kho/abi/luo.h > >> @@ -89,14 +90,14 @@ struct luo_ser { > >> /** > >> * struct luo_file_ser - Represents the serialized preserves files. > >> * @compatible: File handler compatible string. > >> - * @data: Private data > >> + * @serialized_data: The serialized KHO pointer for this file > > > > I am concerned about layring violation here. > > > > LUO is designed as a generic, opaque transport layer that promises to > > preserve 64 bits of raw data. How those 64 bits are interpreted is > > entirely up to individual clients. > > > > While some clients like memfd_luo will use those 64 bits as a physical > > address pointing to KHO-preserved structures, other clients may store a > > generic token, cookie, index, or non-pointer status. By > > changing u64 data to DECLARE_KHOSER_PTR(serialized_data, void *) in > > struct luo_file_ser, we force KHO pointer semantics and layout > > constraints on all generic LUO files. > > That makes sense theory, but in practice, no file handler is going to > need only 8 bytes for its metadata. It is always going to need more, and > to store more information, it needs to store a pointer to that > information with the 64 bits it gets. > > Do you have any examples of something else one might store here? > > At least looking at the current file handlers merged and in flight, > memfd, iommufd, vfio, pci, hugetlb, guest_memfd, all of them store a > pointer here. Right, and all of those types are private to file-handlers, not to LUO, so my question is: > > And if everyone is only storing pointers in this field, might as well > give them a bit of type safety. How khoser helps void * type? Pasha > > > > > Clients that need KHO pointer serialization must cast that opaque 64-bit > > value to/from a KHOSER_PTR within their own callbacks. > > > > Also, the field descriptions in struct luo_file_ser are no longer > > aligned due to the length of the new variable name, I believe it will > > cause warning when making docs. > > -- > Regards, > Pratyush Yadav