On Tue, Dec 11, 2018 at 10:55:59AM +0100, Greg Kurz wrote: > On Tue, 11 Dec 2018 14:53:32 +1100 > Alexey Kardashevskiy <[email protected]> wrote: > > > On 10/12/2018 20:30, Greg Kurz wrote: > > > On Mon, 10 Dec 2018 17:20:43 +1100 > > > David Gibson <[email protected]> wrote: > > > > > >> On Mon, Nov 12, 2018 at 03:12:26PM +1100, Alexey Kardashevskiy wrote: > > >>> > > >>> > > >>> On 12/11/2018 05:10, Greg Kurz wrote: > > >>>> Hi Alexey, > > >>>> > > >>>> Just a few remarks. See below. > > >>>> > > >>>> On Thu, 8 Nov 2018 12:44:06 +1100 > > >>>> Alexey Kardashevskiy <[email protected]> wrote: > > >>>> > > >>>>> SLOF receives a device tree and updates it with various properties > > >>>>> before switching to the guest kernel and QEMU is not aware of any > > >>>>> changes > > >>>>> made by SLOF. Since there is no real RTAS (QEMU implements it), it > > >>>>> makes > > >>>>> sense to pass the SLOF final device tree to QEMU to let it implement > > >>>>> RTAS related tasks better, such as PCI host bus adapter hotplug. > > >>>>> > > >>>>> Specifially, now QEMU can find out the actual XICS phandle (for PHB > > >>>>> hotplug) and the RTAS linux,rtas-entry/base properties (for firmware > > >>>>> assisted NMI - FWNMI). > > >>>>> > > >>>>> This stores the initial DT blob in the sPAPR machine and replaces it > > >>>>> in the KVMPPC_H_UPDATE_DT (new private hypercall) handler. > > >>>>> > > >>>>> This adds an @update_dt_enabled machine property to allow backward > > >>>>> migration. > > >>>>> > > >>>>> SLOF already has a hypercall since > > >>>>> https://github.com/aik/SLOF/commit/e6fc84652c9c0073f9183 > > >>>>> > > >>>>> Signed-off-by: Alexey Kardashevskiy <[email protected]> > > >>>>> --- > > >>>>> include/hw/ppc/spapr.h | 7 ++++++- > > >>>>> hw/ppc/spapr.c | 29 ++++++++++++++++++++++++++++- > > >>>>> hw/ppc/spapr_hcall.c | 32 ++++++++++++++++++++++++++++++++ > > >>>>> hw/ppc/trace-events | 2 ++ > > >>>>> 4 files changed, 68 insertions(+), 2 deletions(-) > > >>>>> > > >>>>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h > > >>>>> index ad4d7cfd97..f5dcaf44cb 100644 > > >>>>> --- a/include/hw/ppc/spapr.h > > >>>>> +++ b/include/hw/ppc/spapr.h > > >>>>> @@ -100,6 +100,7 @@ struct sPAPRMachineClass { > > >>>>> > > >>>>> /*< public >*/ > > >>>>> bool dr_lmb_enabled; /* enable dynamic-reconfig/hotplug of > > >>>>> LMBs */ > > >>>>> + bool update_dt_enabled; /* enable KVMPPC_H_UPDATE_DT */ > > >>>>> bool use_ohci_by_default; /* use USB-OHCI instead of XHCI */ > > >>>>> bool pre_2_10_has_unused_icps; > > >>>>> bool legacy_irq_allocation; > > >>>>> @@ -136,6 +137,9 @@ struct sPAPRMachineState { > > >>>>> int vrma_adjust; > > >>>>> ssize_t rtas_size; > > >>>>> void *rtas_blob; > > >>>>> + uint32_t fdt_size; > > >>>>> + uint32_t fdt_initial_size; > > >>>> > > >>>> I don't quite see the purpose of fdt_initial_size... it seems to be > > >>>> only > > >>>> used to print a trace. > > >>> > > >>> > > >>> Ah, lost in rebase. The purpose was to test if the new device tree has > > >>> not grown too much. > > >>> > > >>> > > >>> > > >>>> > > >>>>> + void *fdt_blob; > > >>>>> long kernel_size; > > >>>>> bool kernel_le; > > >>>>> uint32_t initrd_base; > > >>>>> @@ -462,7 +466,8 @@ struct sPAPRMachineState { > > >>>>> #define KVMPPC_H_LOGICAL_MEMOP (KVMPPC_HCALL_BASE + 0x1) > > >>>>> /* Client Architecture support */ > > >>>>> #define KVMPPC_H_CAS (KVMPPC_HCALL_BASE + 0x2) > > >>>>> -#define KVMPPC_HCALL_MAX KVMPPC_H_CAS > > >>>>> +#define KVMPPC_H_UPDATE_DT (KVMPPC_HCALL_BASE + 0x3) > > >>>>> +#define KVMPPC_HCALL_MAX KVMPPC_H_UPDATE_DT > > >>>>> > > >>>>> typedef struct sPAPRDeviceTreeUpdateHeader { > > >>>>> uint32_t version_id; > > >>>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > > >>>>> index c08130facb..5e2d4d211c 100644 > > >>>>> --- a/hw/ppc/spapr.c > > >>>>> +++ b/hw/ppc/spapr.c > > >>>>> @@ -1633,7 +1633,10 @@ static void spapr_machine_reset(void) > > >>>>> /* Load the fdt */ > > >>>>> qemu_fdt_dumpdtb(fdt, fdt_totalsize(fdt)); > > >>>>> cpu_physical_memory_write(fdt_addr, fdt, fdt_totalsize(fdt)); > > >>>>> - g_free(fdt); > > >>>>> + g_free(spapr->fdt_blob); > > >>>>> + spapr->fdt_size = fdt_totalsize(fdt); > > >>>>> + spapr->fdt_initial_size = spapr->fdt_size; > > >>>>> + spapr->fdt_blob = fdt; > > >>>> > > >>>> Hmm... It looks weird to store state in a reset handler. I'd rather > > >>>> zeroe > > >>>> both fdt_blob and fdt_size here. > > >>> > > >>> The device tree is built from the reset handler and the idea is that we > > >>> want to always have some tree in the machine. > > >> > > >> Yes, I think the approach here is fine. Otherwise when we want to > > >> look up the current fdt state in RTAS calls or whatever we'd always > > >> have to do > > >> if (fdt_blob) > > >> look up that > > >> else > > >> look up qemu created fdt. > > >> > > > > > > No. We only have one fdt blob: the initial one, I'd rather > > > call reset time one, or the updated one. > > > > There is one fdt in the machine, always. Either initial or from cas. > > Yeah, reset time fdt is either the initial one, either cas... and I'm now > wandering what happens if migration occurs between cas that sets cas_reboot > and the corresponding reset. With the current code base, I have the impression > that the destination will redo the full cas+cas_reboot cycle after restart or > am I missing something ?
Yes, I believe that's correct. It's kind of an edge case and that CAS
cycle should still complete ok, it'll just take a little longer to
boot, so I thought that was preferable to the complexity of migrating
the CAS state.
> > >> Incidentally 'fdt' and 'fdt_blob' names do a terrible job of
> > >> distinguishing what the difference is. Renaming fdt to fdt_initial
> > >> (to match fdt_initial_size) and fdt_blob to fdt should make that
> > >> clearer.
> > >>
> > >
> > > As mentioned earlier in this thread, spapr->fdt_initial_size is only used
> > > for tracing if the received fdt blob fails fdt_check_full()...
> > >
> > > $ git grep -H fdt_initial_size
> > > hw/ppc/spapr.c: spapr->fdt_initial_size = spapr->fdt_size;
> > > hw/ppc/spapr.c: VMSTATE_UINT32(fdt_initial_size,
> > > sPAPRMachineState),
> > > hw/ppc/spapr_hcall.c:
> > > trace_spapr_update_dt_failed(spapr->fdt_initial_size, cb,
> > > include/hw/ppc/spapr.h: uint32_t fdt_initial_size;
> > >
> > > Not sure it is helpful, and anyway, it is expected to be the same in
> > > source
> > > and destination, so why put it in the migration stream ?
> >
> >
> > Well, we do build the fdt anyway even when receive migration but we do
> > not have to and yes we can expect the fdt on the destination to be of
> > the same size since it is the same command line, it is just guessing and
> > expecting vs. knowing and I prefer the latter as the reset time fdt and
> > migration source fdt might have different size because of
> > host-model/host-serial/slot-label/similar properties.
>
> Right but I still don't see the usefulness of fdt_initial_size...
So, it's there to address exactly the problem you pointed out elswhere
in the thread: the idea was to disallow the guest resubmitting an fdt
which is "too much" bigger than the original one, thereby consuming a
bunch of qemu memory. The thought was that this is a bit more robust
that just checking against a fixed max size, especially if we need to
increase that fixed size in future to handle really big partitions.
> > > The only case where we want to migrate something is when h_update_dt() has
> > > succeeded, ie, the guest passed a valid DT blob. This implies that its
> > > size isn't 0, otherwise fdt_check_full() would return -FDT_ERR_TRUNCATED.
> > >
> > > I would suggest rather to:
> > >
> > > - completely drop spapr->fdt_initial_size
> > > - clear spapr->fdt_size at machine reset
> > > - migrate if spapr->fdt_size is not zero
> > >
> > > Also, I've just realized another problem... nothing prevents a malicious
> > > guest to pass an insanely great size to h_update_dt, which would cause
> > > g_malloc0() to abort... The passed size should be checked against
> > > FDT_MAX_SIZE.
> >
> > Good point. Just noticed - as posted, the checker actually checks the
> > reset time tree, not the updated one, my bad :)
> >
> >
> >
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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