Re: [Qemu-devel] [PATCH v7 09/19] spapr: add device tree support for the XIVE exploitation mode

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Dec 11, 2018 at 10:06:46AM +0100, Cédric Le Goater wrote:
> On 12/11/18 1:38 AM, David Gibson wrote:
> > On Mon, Dec 10, 2018 at 08:53:17AM +0100, Cédric Le Goater wrote:
> >> On 12/10/18 7:39 AM, David Gibson wrote:
> >>> On Sun, Dec 09, 2018 at 08:46:00PM +0100, Cédric Le Goater wrote:
> >>>> The XIVE interface for the guest is described in the device tree under
> >>>> the "interrupt-controller" node. A couple of new properties are
> >>>> specific to XIVE :
> >>>>
> >>>>  - "reg"
> >>>>
> >>>>    contains the base address and size of the thread interrupt
> >>>>    managnement areas (TIMA), for the User level and for the Guest OS
> >>>>    level. Only the Guest OS level is taken into account today.
> >>>>
> >>>>  - "ibm,xive-eq-sizes"
> >>>>
> >>>>    the size of the event queues. One cell per size supported, contains
> >>>>    log2 of size, in ascending order.
> >>>>
> >>>>  - "ibm,xive-lisn-ranges"
> >>>>
> >>>>    the IRQ interrupt number ranges assigned to the guest for the IPIs.
> >>>>
> >>>> and also under the root node :
> >>>>
> >>>>  - "ibm,plat-res-int-priorities"
> >>>>
> >>>>    contains a list of priorities that the hypervisor has reserved for
> >>>>    its own use. OPAL uses the priority 7 queue to automatically
> >>>>    escalate interrupts for all other queues (DD2.X POWER9). So only
> >>>>    priorities [0..6] are allowed for the guest.
> >>>>
> >>>> Extend the sPAPR IRQ backend with a new handler to populate the DT
> >>>> with the appropriate "interrupt-controller" node.
> >>>>
> >>>> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> >>>> ---
> >>>>  include/hw/ppc/spapr_irq.h  |  2 ++
> >>>>  include/hw/ppc/spapr_xive.h |  2 ++
> >>>>  include/hw/ppc/xics.h       |  4 +--
> >>>>  hw/intc/spapr_xive.c        | 64 +++++++++++++++++++++++++++++++++++++
> >>>>  hw/intc/xics_spapr.c        |  3 +-
> >>>>  hw/ppc/spapr.c              |  3 +-
> >>>>  hw/ppc/spapr_irq.c          |  3 ++
> >>>>  7 files changed, 77 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/include/hw/ppc/spapr_irq.h b/include/hw/ppc/spapr_irq.h
> >>>> index 23cdb51b879e..e51e9f052f63 100644
> >>>> --- a/include/hw/ppc/spapr_irq.h
> >>>> +++ b/include/hw/ppc/spapr_irq.h
> >>>> @@ -39,6 +39,8 @@ typedef struct sPAPRIrq {
> >>>>      void (*free)(sPAPRMachineState *spapr, int irq, int num);
> >>>>      qemu_irq (*qirq)(sPAPRMachineState *spapr, int irq);
> >>>>      void (*print_info)(sPAPRMachineState *spapr, Monitor *mon);
> >>>> +    void (*dt_populate)(sPAPRMachineState *spapr, uint32_t nr_servers,
> >>>> +                        void *fdt, uint32_t phandle);
> >>>>  } sPAPRIrq;
> >>>>  
> >>>>  extern sPAPRIrq spapr_irq_xics;
> >>>> diff --git a/include/hw/ppc/spapr_xive.h b/include/hw/ppc/spapr_xive.h
> >>>> index 9506a8f4d10a..728a5e8dc163 100644
> >>>> --- a/include/hw/ppc/spapr_xive.h
> >>>> +++ b/include/hw/ppc/spapr_xive.h
> >>>> @@ -45,5 +45,7 @@ qemu_irq spapr_xive_qirq(sPAPRXive *xive, uint32_t lisn);
> >>>>  typedef struct sPAPRMachineState sPAPRMachineState;
> >>>>  
> >>>>  void spapr_xive_hcall_init(sPAPRMachineState *spapr);
> >>>> +void spapr_dt_xive(sPAPRMachineState *spapr, uint32_t nr_servers, void *fdt,
> >>>> +                   uint32_t phandle);
> >>>>  
> >>>>  #endif /* PPC_SPAPR_XIVE_H */
> >>>> diff --git a/include/hw/ppc/xics.h b/include/hw/ppc/xics.h
> >>>> index 9958443d1984..14afda198cdb 100644
> >>>> --- a/include/hw/ppc/xics.h
> >>>> +++ b/include/hw/ppc/xics.h
> >>>> @@ -181,8 +181,6 @@ typedef struct XICSFabricClass {
> >>>>      ICPState *(*icp_get)(XICSFabric *xi, int server);
> >>>>  } XICSFabricClass;
> >>>>  
> >>>> -void spapr_dt_xics(int nr_servers, void *fdt, uint32_t phandle);
> >>>> -
> >>>>  ICPState *xics_icp_get(XICSFabric *xi, int server);
> >>>>  
> >>>>  /* Internal XICS interfaces */
> >>>> @@ -204,6 +202,8 @@ void icp_resend(ICPState *ss);
> >>>>  
> >>>>  typedef struct sPAPRMachineState sPAPRMachineState;
> >>>>  
> >>>> +void spapr_dt_xics(sPAPRMachineState *spapr, uint32_t nr_servers, void *fdt,
> >>>> +                   uint32_t phandle);
> >>>>  int xics_kvm_init(sPAPRMachineState *spapr, Error **errp);
> >>>>  void xics_spapr_init(sPAPRMachineState *spapr);
> >>>>  
> >>>> diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
> >>>> index 982ac6e17051..a6d854b07690 100644
> >>>> --- a/hw/intc/spapr_xive.c
> >>>> +++ b/hw/intc/spapr_xive.c
> >>>> @@ -14,6 +14,7 @@
> >>>>  #include "target/ppc/cpu.h"
> >>>>  #include "sysemu/cpus.h"
> >>>>  #include "monitor/monitor.h"
> >>>> +#include "hw/ppc/fdt.h"
> >>>>  #include "hw/ppc/spapr.h"
> >>>>  #include "hw/ppc/spapr_xive.h"
> >>>>  #include "hw/ppc/xive.h"
> >>>> @@ -1381,3 +1382,66 @@ void spapr_xive_hcall_init(sPAPRMachineState *spapr)
> >>>>      spapr_register_hypercall(H_INT_SYNC, h_int_sync);
> >>>>      spapr_register_hypercall(H_INT_RESET, h_int_reset);
> >>>>  }
> >>>> +
> >>>> +void spapr_dt_xive(sPAPRMachineState *spapr, uint32_t nr_servers, void *fdt,
> >>>> +                   uint32_t phandle)
> >>>> +{
> >>>> +    sPAPRXive *xive = spapr->xive;
> >>>> +    int node;
> >>>> +    uint64_t timas[2 * 2];
> >>>> +    /* Interrupt number ranges for the IPIs */
> >>>> +    uint32_t lisn_ranges[] = {
> >>>> +        cpu_to_be32(0),
> >>>> +        cpu_to_be32(nr_servers),
> >>>> +    };
> >>>> +    uint32_t eq_sizes[] = {
> >>>> +        cpu_to_be32(12), /* 4K */
> >>>> +        cpu_to_be32(16), /* 64K */
> >>>> +        cpu_to_be32(21), /* 2M */
> >>>> +        cpu_to_be32(24), /* 16M */
> >>>
> >>> For KVM, are we going to need to clamp this list based on the
> >>> pagesizes the guest can use?
> >>
> >> I would say so. Is there a KVM service for that ?
> > 
> > I'm not sure what you mean by a KVM service here.
> 
> I meant a routine giving a list of the possible backing pagesizes.

I'm still not really sure what you mean by that.

> >> Today, the OS scans the list and picks the size fitting its current 
> >> PAGE_SIZE/SHIFT. But I suppose it would be better to advertise 
> >> only the page sizes that QEMU/KVM supports. Or should we play safe 
> >> and only export : 4K, 64K ? 
> > 
> > So, I'm guessing the limitation here is that when we use the KVM XIVE
> > acceleration, the EQ will need to be host-contiguous?  
> 
> The EQ should be a single page (from the specs). So we don't have 
> a contiguity problem.

A single page according to whom, though?  A RPT guest can use 2MiB
pages, even if it is backed with smaller pages on the host, but I'm
guessing it would not work to have its EQ be a 2MiB page, since it
won't be host-contiguous.

> > So, we can't have EQs larger than the backing pagesize for guest 
> > memory.
> >
>  > We try to avoid having guest visible differences based on whether
> > we're using KVM or not, so we don't want to change this list depending
> > on whether KVM is active etc. - or on whether we're backing the guest
> > with hugepages.
> > 
> > We could reuse the cap-hpt-max-page-size machine parameter which also
> > relates to backing page size, but that might be confusing since it's
> > explicitly about HPT only whereas this limitation would apply to RPT
> > guests too, IIUC.
> > 
> > I think our best bet is probably to limit to 64kiB queues
> > unconditionally.  
> 
> OK. That's the default. We can refine this list of page sizes later on
> when we introduce KVM support if needed.
> 
> > AIUI, that still gives us 8192 slots in the queue,
> 
> The entries are 32bits. So that's 16384 entries. 

Even better.

> > which is enough to store one of every possible irq, which should be
> > enough.
> 
> yes. 
> 
> I don't think Linux measures how much entries are dequeued at once.
> It would give us a feel of how much pressure these EQs can sustain.
> 
> C.
>  
> > There's still an issue if we have a 4kiB pagesize host kernel, but we
> > could just disable kernel_irqchip in that situation, since we don't
> > expect people to be using that much in practice.
> > 
> >>>> +    };
> >>>> +    /* The following array is in sync with the reserved priorities
> >>>> +     * defined by the 'spapr_xive_priority_is_reserved' routine.
> >>>> +     */
> >>>> +    uint32_t plat_res_int_priorities[] = {
> >>>> +        cpu_to_be32(7),    /* start */
> >>>> +        cpu_to_be32(0xf8), /* count */
> >>>> +    };
> >>>> +    gchar *nodename;
> >>>> +
> >>>> +    /* Thread Interrupt Management Area : User (ring 3) and OS (ring 2) */
> >>>> +    timas[0] = cpu_to_be64(xive->tm_base +
> >>>> +                           XIVE_TM_USER_PAGE * (1ull << TM_SHIFT));
> >>>> +    timas[1] = cpu_to_be64(1ull << TM_SHIFT);
> >>>> +    timas[2] = cpu_to_be64(xive->tm_base +
> >>>> +                           XIVE_TM_OS_PAGE * (1ull << TM_SHIFT));
> >>>> +    timas[3] = cpu_to_be64(1ull << TM_SHIFT);
> >>>
> >>> So this gives the MMIO address of the TIMA.  
> >>
> >> Yes. It is considered to be a fixed "address" 
> >>
> >>> Where does the guest get the MMIO address for the ESB pages from?
> >>
> >> with the hcall H_INT_GET_SOURCE_INFO.
> > 
> > Ah, right.
> > 
> 

-- 
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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