Hi On Wed, Sep 19, 2018 at 4:14 PM Dr. David Alan Gilbert <dgilb...@redhat.com> wrote: > > * Igor Mammedov (imamm...@redhat.com) wrote: > > On Wed, 19 Sep 2018 11:58:22 +0100 > > "Dr. David Alan Gilbert" <dgilb...@redhat.com> wrote: > > > > > * Marc-André Lureau (marcandre.lur...@gmail.com) wrote: > > > > Hi > > > > > > > > On Tue, Sep 18, 2018 at 7:49 PM Dr. David Alan Gilbert > > > > <dgilb...@redhat.com> wrote: > > > > > > > > > > * Marc-André Lureau (marcandre.lur...@gmail.com) wrote: > > > > > > Hi > > > > > > > > > > > > On Tue, Sep 11, 2018 at 6:19 PM Laszlo Ersek <ler...@redhat.com> > > > > > > wrote: > > > > > > > > > > > > > > +Alex, due to mention of 21e00fa55f3fd > > > > > > > > > > > > > > On 09/10/18 15:03, Marc-André Lureau wrote: > > > > > > > > Hi > > > > > > > > > > > > > > > > On Mon, Sep 10, 2018 at 2:44 PM Dr. David Alan Gilbert > > > > > > > > <dgilb...@redhat.com> wrote: > > > > > > > >> (I didn't know about guest_phys_block* and would have probably > > > > > > > >> just used > > > > > > > >> qemu_ram_foreach_block ) > > > > > > > >> > > > > > > > > > > > > > > > > guest_phys_block*() seems to fit, as it lists only the blocks > > > > > > > > actually > > > > > > > > used, and already skip the device RAM. > > > > > > > > > > > > > > > > Laszlo, you wrote the functions > > > > > > > > (https://git.qemu.org/?p=qemu.git;a=commit;h=c5d7f60f0614250bd925071e25220ce5958f75d0), > > > > > > > > do you think it's appropriate to list the memory to clear, or we > > > > > > > > should rather use qemu_ram_foreach_block() ? > > > > > > > > > > > > > > Originally, I would have said, "use either, doesn't matter". > > > > > > > Namely, > > > > > > > when I introduced the guest_phys_block*() functions, the original > > > > > > > purpose was not related to RAM *contents*, but to RAM *addresses* > > > > > > > (GPAs). This is evident if you look at the direct child commit of > > > > > > > c5d7f60f0614, namely 56c4bfb3f07f, which put GuestPhysBlockList > > > > > > > to use. > > > > > > > And, for your use case (= wiping RAM), GPAs don't matter, only > > > > > > > contents > > > > > > > matter. > > > > > > > > > > > > > > However, with the commits I mentioned previously, namely > > > > > > > e4dc3f5909ab9 > > > > > > > and 21e00fa55f3fd, we now filter out some RAM blocks from the > > > > > > > dumping > > > > > > > based on contents / backing as well. I think? So I believe we > > > > > > > should > > > > > > > honor that for the wiping to. I guess I'd (vaguely) suggest using > > > > > > > guest_phys_block*(). > > > > > > > > > > > > > > (And then, as Dave suggests, maybe extend the filter to consider > > > > > > > pmem > > > > > > > too, separately.) > > > > > > > > > > > > I looked a bit into skipping pmem memory. The issue is that RamBlock > > > > > > and MemoryRegion have no idea they are actually used for nvram (you > > > > > > could rely on hostmem.pmem flag, but this is optional), and I don't > > > > > > see a clear way to figure this out. > > > > > > > > > > I think the pmem flag is what we should use; the problem though is we > > > > > > > > That would be much simpler. But What if you setup a nvdimm backend by > > > > a non-pmem memory? It will always be cleared? What about platforms > > > > that do not support libpmem? > > > > > > Right, that's basically the problem I say below, the difference between > > > (a) and (b). > > > > > > > > have two different pieces of semantics: > > > > > a) PMEM - needs special flush instruction/calls > > > > > b) PMEM - my data is persistent, please don't clear me > > > > > > > > > > Do those always go together? > > > > > > > > > > (Copying in Junyan He who added the RAM_PMEM flag) > > > > > > > > > > > I can imagine to retrieve the MemoryRegion from guest phys address, > > > > > > then check the owner is TYPE_NVDIMM for example. Is this a good > > > > > > solution? > > > > > > > > > > No, I think it's upto whatever creates the region to set a flag > > > > > somewhere properly - there's no telling whether it'll always be NVDIMM > > > > > or some other object. > > > > > > > > We could make the owner object set a flag on the MemoryRegion, or > > > > implement a common NV interface. > > > > > > I think preferably on the RAMBlock, but yes; the question then is > > > whether we need to split the PMEM flag into two for (a) and (b) above > > > and whether they need to be separately set. > > well, > > I get current pmem flag semantics as backend supports persistent memory > > whether frontend will use it or not is different story. > > > > Perhaps we need a separate flag which say that pmem is in use, > > but what about usecase where nvdimm is used as RAM and not storage > > we probably would like to wipe it out as normal RAM. > > Right, so we're slowly building up the number of flags/policies we're > trying to represent here; it's certainly not the one 'pmem' flag we > currently have. > > > Maybe we should add frontend property to allow selecting policy per device, > > which then could be propagated to MemoryRegion/RAMBlock? > > By 'device' here you mean memory-backend-* objects? If so then yes I'd > agree a property on those propagated to the underlying RAMBlock would > be ideal.
Earlier I was trying to suggest the guest exposed device / owner (dimm/nvdimm etc) would be the one setting a flag. I can work on a patch, that should be more clear. > Dave > > > > Dave > > > > > > > > > > > > > Dave > > > > > > > > > > > There is memory_region_from_host(), is there a > > > > > > memory_region_from_guest() ? > > > > > > > > > > > > thanks > > > > > > > > > > > > > > > > > > -- > > > > > > Marc-André Lureau > > > > > -- > > > > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK > > > > > > > > > > > > > > > > -- > > > > Marc-André Lureau > > > -- > > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK > > > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK -- Marc-André Lureau
