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Subject: Re: [PATCH v2 1/1] virtio-pmem: Support describing pmem as shared memory region
On Tue, Jul 27, 2021 at 05:06:43PM +0200, Cornelia Huck wrote: > On Mon, Jul 26 2021, tstark@linux.microsoft.com wrote: > > > @@ -50,12 +53,29 @@ \subsection{Device Initialization}\label{sec:Device Types / PMEM Device / Device > > File backed memory SHOULD be memory mapped to guest address space with SHARED > > memory mapping. > > > > +If VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the device MUST indicate the > > +guest physical address as a shared memory region. The device MUST use shared > > +memory region ID 0. The device SHOULD set \field{start} and \field{size} to zero. > > + > > +If VIRTIO_PMEM_F_SHMEM_REGION has not been negotiated, the device MUST indicate > > +the guest physical address as a guest absolute address. The device MUST set > > +\field{start} to the absolute address and \field{size} to the size of the > > +address range, in bytes. > > + > > \subsection{Driver Initialization}\label{sec:Device Types / PMEM Driver / Driver Initialization} > > > > Driver hotplugs the physical memory and registers associated > > region with the pmem API. Also, configures a flush callback > > function with the corresponding region. > > > > +\drivernormative{\subsubsection}{Driver Initialization}{Device Types / PMEM Driver / Driver Initialization} > > + > > +The driver SHOULD query the physical address ranges where the pmem was mapped. > > Isn't the driver quite useless if it doesn't discover where the pmem can > be found? I'm not sure we need that sentence. It's about as useful as a paperweight if it doesn't discover where the pmem was mapped :) Agreed, this isn't necessary. > > +If VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the driver SHOULD query > > +shared memory ID 0 for the physical address ranges and MUST NOT use \field{start} > > +or \field{size}. Else, the driver SHOULD read the physical address ranges from > > +\field{start} and \field{size}. > > 'SHOULD' is probably not the right way to specify this. What about the > following: > > "In order to discover the physical address ranges where the pmem was > mapped: > > If VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the driver MUST query > shared memory ID 0 for the physical address ranges, and MUST NOT use > \field{start} or \field{stop}. > > If VIRTIO_PMEM_F_SHMEM_REGION has not been negotiated, the driver MUST > read the physical address ranges from \field{start} and \field{stop}." Sounds great to me. Will update in v3. Thanks again for the advice. Thanks, Taylor
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