On Thu, Apr 30, 2020 at 1:21 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > >> Just because we decided to use some DAX memory in the current kernel as > >> system ram, doesn't mean we should make that decision for the kexec > >> kernel (e.g., using it as initial memory, placing kexec binaries onto > >> it, etc.). This is also not what we would observe during a real reboot. > > > > Agree. > > > >> I can see that the "System RAM" resource will show up as child resource > >> under the device e.g., in /proc/iomem. > >> > >> However, entries in /sys/firmware/memmap/ are created as "System RAM". > > > > True. Do you think this rename should just be limited to what type > > /sys/firmware/memmap/ emits? I have the concern, but no proof > > We could split this patch into > > MHP_NO_FIRMWARE_MEMMAP (create firmware memmap entries) > > and > > MHP_DRIVER_MANAGED (name of the resource) > > See below, the latter might not be needed. > > > currently, that there are /proc/iomem walkers that explicitly look for > > "System RAM", but might be thrown off by "System RAM (driver > > managed)". I was not aware of /sys/firmware/memmap until about 5 > > minutes ago. > > The only two users of /proc/iomem I am aware of are kexec-tools and some > s390x tools. > > kexec-tools on x86-64 uses /sys/firmware/memmap to craft the initial > memmap, but uses /proc/iomem to > a) Find places for kexec images > b) Detect memory regions to dump via kdump > > I am not yet sure if we really need the "System RAM (driver managed)" > part. If we can teach kexec-tools to > a) Don't place kexec images on "System RAM" that has a parent resource > (most likely requires kexec-tools changes) > b) Consider for kdump "System RAM" that has a parent resource > we might be able to avoid renaming that. (I assume that's already done) > > E.g., regarding virtio-mem (patch #3) I am currently also looking into > creating a parent resource instead, like dax/kmem to avoid the rename: > > :/# cat /proc/iomem > 00000000-00000fff : Reserved > [...] > 100000000-13fffffff : System RAM > 140000000-33fffffff : virtio0 > 140000000-147ffffff : System RAM > 148000000-14fffffff : System RAM > 150000000-157ffffff : System RAM > 340000000-303fffffff : virtio1 > 340000000-347ffffff : System RAM > 3280000000-32ffffffff : PCI Bus 0000:00 Looks good to me if it flies with kexec-tools.
