Re: [Qemu-devel] [PATCH v2] piix: define a TOM register to report the base of PCI

[Stefano Stabellini]

Right, I think that reading as 0xff and write once would be important
improvements for this patch.

I would like to see a document somewhere (maybe just a text file under
xen-unstable/docs/misc) with a list of deviations of the i440fx we
emulate and the real one.

Other than that, it would be OK for me.

On Tue, 26 Feb 2013, Zhang, Xiantao wrote:
> For real i440fx, its TOM is fixed to 1G, I think Xen or other VMMs playing 
> with Qemu should break this hardware rule.  Maybe we can implement this 
> register as a write-only one, so that OS can't see its existence.   If OS 
> reads this register, Qemu always return 0xff, and for any write operations to 
> this register, it may impact hardware's behavior.  This conforms to the 
> behavior of OS accessing a reserved register.
> Xiantao
> 
> > -----Original Message-----
> > From: address@hidden
> > [mailto:address@hidden On Behalf
> > Of Hao, Xudong
> > Sent: Tuesday, February 26, 2013 11:33 AM
> > To: Stefano Stabellini; Ian Campbell
> > Cc: address@hidden; address@hidden; address@hidden; xen-
> > address@hidden; address@hidden; address@hidden
> > Subject: Re: [Qemu-devel] [PATCH v2] piix: define a TOM register to report 
> > the
> > base of PCI
> >
> > > -----Original Message-----
> > > From: address@hidden
> > > [mailto:address@hidden On Behalf
> > > Of Stefano Stabellini
> > > Sent: Tuesday, February 26, 2013 12:06 AM
> > > To: Hao, Xudong
> > > Cc: address@hidden; Stefano Stabellini; address@hidden;
> > > address@hidden; address@hidden; address@hidden;
> > > address@hidden
> > > Subject: Re: [Qemu-devel] [PATCH v2] piix: define a TOM register to report
> > the
> > > base of PCI
> > >
> > > On Mon, 25 Feb 2013, Xudong Hao wrote:
> > > > v2:
> > > > * Use "piix: " in the subject rather than "qemu: "
> > > > * Define TOM register as one byte
> > > > * Define default TOM value instead of hardcode 0xe0000000 in more that
> > one
> > > place
> > > > * Use API pci_set_byte for pci config access
> > > > * Use dev->config instead of the indirect d->dev.config
> > > >
> > > > Define a TOM(top of memory) register to report the base of PCI memory,
> > > update
> > > > memory region dynamically. TOM register are defined to one byte in PCI
> > > configure
> > > > space, because that only upper 4 bit of PCI memory takes effect for 
> > > > Xen, so
> > > > it requires bios set TOM with 16M-aligned.
> > > >
> > > > Signed-off-by: Xudong Hao <address@hidden>
> > > > Signed-off-by: Xiantao Zhang <address@hidden>
> > >
> > > The patch is OK from my POV, but I think that Ian raised a valid
> > > concern: we are supposed to emulate a real piece of hardware, maybe
> > > another mechanism (xenbus? hvmop?) to pass the information from
> > > hvmloader to QEMU would be a better fit than this.
> > > Otherwise at least we would need to advertize this feature somehow: if
> > > hvmloader can use it, the guest kernel can use it too...
> > >
> > Hi, Ian and Stefano
> >
> > Here adding this faking register in bios is a hack way.
> > However, what we emulated is not full real piece of hardware at all times, 
> > the
> > max of TOM for i440fx is 1G, and we already adjust the TOM in qemu.
> > The faking register is only effective by bios and device model. This 
> > register is
> > reserved by host bridge, so guest can't access this register, guest kernel 
> > should
> > handle well when accessing a reserved region.
> >
> > -Thanks
> > Xudong
> > >
> > >
> > > >  hw/pc.h       |  7 +++---
> > > >  hw/pc_piix.c  | 12 +++-------
> > > >  hw/piix_pci.c | 73
> > > +++++++++++++++++++++++++++++++++++++++++++----------------
> > > >  3 files changed, 59 insertions(+), 33 deletions(-)
> > > >
> > > > diff --git a/hw/pc.h b/hw/pc.h
> > > > index fbcf43d..62adcc5 100644
> > > > --- a/hw/pc.h
> > > > +++ b/hw/pc.h
> > > > @@ -129,15 +129,14 @@ extern int no_hpet;
> > > >  struct PCII440FXState;
> > > >  typedef struct PCII440FXState PCII440FXState;
> > > >
> > > > +#define I440FX_TOM     0xe0000000
> > > > +#define I440FX_XEN_TOM 0xf0000000
> > > > +
> > > >  PCIBus *i440fx_init(PCII440FXState **pi440fx_state, int *piix_devfn,
> > > >                      ISABus **isa_bus, qemu_irq *pic,
> > > >                      MemoryRegion *address_space_mem,
> > > >                      MemoryRegion *address_space_io,
> > > >                      ram_addr_t ram_size,
> > > > -                    hwaddr pci_hole_start,
> > > > -                    hwaddr pci_hole_size,
> > > > -                    hwaddr pci_hole64_start,
> > > > -                    hwaddr pci_hole64_size,
> > > >                      MemoryRegion *pci_memory,
> > > >                      MemoryRegion *ram_memory);
> > > >
> > > > diff --git a/hw/pc_piix.c b/hw/pc_piix.c
> > > > index 0a6923d..2eef510 100644
> > > > --- a/hw/pc_piix.c
> > > > +++ b/hw/pc_piix.c
> > > > @@ -93,9 +93,9 @@ static void pc_init1(MemoryRegion *system_memory,
> > > >          kvmclock_create();
> > > >      }
> > > >
> > > > -    if (ram_size >= 0xe0000000 ) {
> > > > -        above_4g_mem_size = ram_size - 0xe0000000;
> > > > -        below_4g_mem_size = 0xe0000000;
> > > > +    if (ram_size >= I440FX_TOM) {
> > > > +        above_4g_mem_size = ram_size - I440FX_TOM;
> > > > +        below_4g_mem_size = I440FX_TOM;
> > > >      } else {
> > > >          above_4g_mem_size = 0;
> > > >          below_4g_mem_size = ram_size;
> > > > @@ -130,12 +130,6 @@ static void pc_init1(MemoryRegion
> > > *system_memory,
> > > >      if (pci_enabled) {
> > > >          pci_bus = i440fx_init(&i440fx_state, &piix3_devfn, &isa_bus, 
> > > > gsi,
> > > >                                system_memory, system_io,
> > > ram_size,
> > > > -                              below_4g_mem_size,
> > > > -                              0x100000000ULL -
> > > below_4g_mem_size,
> > > > -                              0x100000000ULL +
> > > above_4g_mem_size,
> > > > -                              (sizeof(hwaddr) == 4
> > > > -                               ? 0
> > > > -                               : ((uint64_t)1 << 62)),
> > > >                                pci_memory, ram_memory);
> > > >      } else {
> > > >          pci_bus = NULL;
> > > > diff --git a/hw/piix_pci.c b/hw/piix_pci.c
> > > > index 3d79c73..3e5a25c 100644
> > > > --- a/hw/piix_pci.c
> > > > +++ b/hw/piix_pci.c
> > > > @@ -86,6 +86,14 @@ struct PCII440FXState {
> > > >  #define I440FX_PAM_SIZE 7
> > > >  #define I440FX_SMRAM    0x72
> > > >
> > > > +/* The maximum vaule of TOM(top of memory) register in I440FX
> > > > + * is 1G, so it doesn't meet any popular virutal machines, so
> > > > + * define another register to report the base of PCI memory.
> > > > + * Use one byte 0xb0 for the upper 8 bit, they are originally
> > > > + * resevered for host bridge.
> > > > + * */
> > > > +#define I440FX_PCI_HOLE_BASE 0xb0
> > > > +
> > > >  static void piix3_set_irq(void *opaque, int pirq, int level);
> > > >  static PCIINTxRoute piix3_route_intx_pin_to_irq(void *opaque, int
> > > pci_intx);
> > > >  static void piix3_write_config_xen(PCIDevice *dev,
> > > > @@ -101,6 +109,43 @@ static int pci_slot_get_pirq(PCIDevice *pci_dev, 
> > > > int
> > > pci_intx)
> > > >      return (pci_intx + slot_addend) & 3;
> > > >  }
> > > >
> > > > +
> > > > +static void i440fx_update_pci_mem_hole(PCII440FXState *f, bool del)
> > > > +{
> > > > +    ram_addr_t above_4g_mem_size;
> > > > +    hwaddr pci_hole_start, pci_hole_size, pci_hole64_start,
> > > pci_hole64_size;
> > > > +
> > > > +    pci_hole_start = pci_default_read_config(&f->dev,
> > > I440FX_PCI_HOLE_BASE, 1) << 24;
> > > > +    pci_hole_size = 0x100000000ULL - pci_hole_start;
> > > > +
> > > > +    if (ram_size >= pci_hole_start) {
> > > > +        above_4g_mem_size = ram_size - pci_hole_start;
> > > > +    } else {
> > > > +        above_4g_mem_size = 0;
> > > > +    }
> > > > +    pci_hole64_start = 0x100000000ULL + above_4g_mem_size;
> > > > +    pci_hole64_size = sizeof(hwaddr) == 4 ? 0 : ((uint64_t)1 << 62);
> > > > +
> > > > +    if (del) {
> > > > +        memory_region_del_subregion(f->system_memory,
> > > &f->pci_hole);
> > > > +        if (pci_hole64_size) {
> > > > +            memory_region_del_subregion(f->system_memory,
> > > &f->pci_hole_64bit);
> > > > +        }
> > > > +    }
> > > > +
> > > > +    memory_region_init_alias(&f->pci_hole, "pci-hole",
> > > f->pci_address_space,
> > > > +                             pci_hole_start, pci_hole_size);
> > > > +    memory_region_add_subregion(f->system_memory, pci_hole_start,
> > > &f->pci_hole);
> > > > +    memory_region_init_alias(&f->pci_hole_64bit, "pci-hole64",
> > > > +                             f->pci_address_space,
> > > > +                             pci_hole64_start, pci_hole64_size);
> > > > +    if (pci_hole64_size) {
> > > > +        memory_region_add_subregion(f->system_memory,
> > > pci_hole64_start,
> > > > +                                    &f->pci_hole_64bit);
> > > > +    }
> > > > +}
> > > > +
> > > > +
> > > >  static void i440fx_update_memory_mappings(PCII440FXState *d)
> > > >  {
> > > >      int i;
> > > > @@ -136,6 +181,9 @@ static void i440fx_write_config(PCIDevice *dev,
> > > >          range_covers_byte(address, len, I440FX_SMRAM)) {
> > > >          i440fx_update_memory_mappings(d);
> > > >      }
> > > > +    if (range_covers_byte(address, len, I440FX_PCI_HOLE_BASE)) {
> > > > +        i440fx_update_pci_mem_hole(d, true);
> > > > +    }
> > > >  }
> > > >
> > > >  static int i440fx_load_old(QEMUFile* f, void *opaque, int version_id)
> > > > @@ -203,6 +251,10 @@ static int i440fx_initfn(PCIDevice *dev)
> > > >
> > > >      d->dev.config[I440FX_SMRAM] = 0x02;
> > > >
> > > > +    /* Emulate top of memory, here use 0xe0000000 as default val*/
> > > > +    uint32_t addr = xen_enabled() ? I440FX_XEN_TOM : I440FX_TOM;
> > > > +    pci_set_byte(dev->config + I440FX_PCI_HOLE_BASE, (uint8_t)(addr >>
> > > 24));
> > > > +
> > > >      cpu_smm_register(&i440fx_set_smm, d);
> > > >      return 0;
> > > >  }
> > > > @@ -214,10 +266,6 @@ static PCIBus *i440fx_common_init(const char
> > > *device_name,
> > > >                                    MemoryRegion
> > > *address_space_mem,
> > > >                                    MemoryRegion
> > > *address_space_io,
> > > >                                    ram_addr_t ram_size,
> > > > -                                  hwaddr pci_hole_start,
> > > > -                                  hwaddr pci_hole_size,
> > > > -                                  hwaddr pci_hole64_start,
> > > > -                                  hwaddr pci_hole64_size,
> > > >                                    MemoryRegion
> > > *pci_address_space,
> > > >                                    MemoryRegion *ram_memory)
> > > >  {
> > > > @@ -244,16 +292,6 @@ static PCIBus *i440fx_common_init(const char
> > > *device_name,
> > > >      f->system_memory = address_space_mem;
> > > >      f->pci_address_space = pci_address_space;
> > > >      f->ram_memory = ram_memory;
> > > > -    memory_region_init_alias(&f->pci_hole, "pci-hole",
> > > f->pci_address_space,
> > > > -                             pci_hole_start, pci_hole_size);
> > > > -    memory_region_add_subregion(f->system_memory, pci_hole_start,
> > > &f->pci_hole);
> > > > -    memory_region_init_alias(&f->pci_hole_64bit, "pci-hole64",
> > > > -                             f->pci_address_space,
> > > > -                             pci_hole64_start, pci_hole64_size);
> > > > -    if (pci_hole64_size) {
> > > > -        memory_region_add_subregion(f->system_memory,
> > > pci_hole64_start,
> > > > -                                    &f->pci_hole_64bit);
> > > > -    }
> > > >      memory_region_init_alias(&f->smram_region, "smram-region",
> > > >                               f->pci_address_space, 0xa0000,
> > > 0x20000);
> > > >      memory_region_add_subregion_overlap(f->system_memory,
> > > 0xa0000,
> > > > @@ -295,6 +333,7 @@ static PCIBus *i440fx_common_init(const char
> > > *device_name,
> > > >      (*pi440fx_state)->dev.config[0x57]=ram_size;
> > > >
> > > >      i440fx_update_memory_mappings(f);
> > > > +    i440fx_update_pci_mem_hole(f, false);
> > > >
> > > >      return b;
> > > >  }
> > > > @@ -304,10 +343,6 @@ PCIBus *i440fx_init(PCII440FXState
> > > **pi440fx_state, int *piix3_devfn,
> > > >                      MemoryRegion *address_space_mem,
> > > >                      MemoryRegion *address_space_io,
> > > >                      ram_addr_t ram_size,
> > > > -                    hwaddr pci_hole_start,
> > > > -                    hwaddr pci_hole_size,
> > > > -                    hwaddr pci_hole64_start,
> > > > -                    hwaddr pci_hole64_size,
> > > >                      MemoryRegion *pci_memory, MemoryRegion
> > > *ram_memory)
> > > >
> > > >  {
> > > > @@ -315,8 +350,6 @@ PCIBus *i440fx_init(PCII440FXState **pi440fx_state,
> > > int *piix3_devfn,
> > > >
> > > >      b = i440fx_common_init("i440FX", pi440fx_state, piix3_devfn, 
> > > > isa_bus,
> > > pic,
> > > >                             address_space_mem, address_space_io,
> > > ram_size,
> > > > -                           pci_hole_start, pci_hole_size,
> > > > -                           pci_hole64_start, pci_hole64_size,
> > > >                             pci_memory, ram_memory);
> > > >      return b;
> > > >  }
> > > > --
> > > > 1.7.12.1
> > > >
> >
>