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[47.54.130.67]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8cc80deae74sm46895946d6.11.2026.05.23.06.29.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 May 2026 06:29:57 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wQmQO-00000006HXM-46jw; Sat, 23 May 2026 10:29:56 -0300 Date: Sat, 23 May 2026 10:29:56 -0300 From: Jason Gunthorpe To: Pranjal Shrivastava Cc: David Matlack , Samiullah Khawaja , David Woodhouse , Lu Baolu , Joerg Roedel , Will Deacon , 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 , Andrew Morton , Chris Li , Vipin Sharma , YiFei Zhu Subject: Re: [PATCH v2 02/16] iommu: Implement IOMMU Live update FLB callbacks Message-ID: <20260523132956.GG7702@ziepe.ca> References: <20260427175633.1978233-1-skhawaja@google.com> <20260427175633.1978233-3-skhawaja@google.com> Precedence: bulk X-Mailing-List: linux-kernel@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: On Mon, May 18, 2026 at 11:52:34AM +0000, Pranjal Shrivastava wrote: > On Fri, May 01, 2026 at 09:45:19PM +0000, David Matlack wrote: > > [...] > > > > + > > > +/** > > > + * struct iommu_hdr_ser - Common header for all serialized IOMMU objects > > > + * @ref_count: Reference count for the object > > > + * @deleted: Flag indicating if the object is deleted > > > + * @incoming: Flag indicating if the object was preserved in previous kernel > > > + */ > > > +struct iommu_hdr_ser { > > > + u32 ref_count; > > > + u32 deleted:1; > > > + u32 incoming:1; > > > > Are C bitfields safe to use in Live Update ABI? > > > > AFAIU, they aren't. The C standard does not dictate how bitfields are > packed into their underlying types (e.g., whether they are packed MSB to > LSB or vice-versa), making them highly dependent on the compiler and arch > endianness. Bitfield are defined in the SYSV UNIX ELF ABIs, they are stable for kexec, but variable across arches how they lay out in memory. Jason