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

["Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>]

> Given that Xen has at least two other mechanisms (xenstore and
> hvmparams) for passing this sort of information around I'm not sure why
> hacking the emulated i440fx device should be the preferred option.

Actually, even in hardware,  I believe there are many registers which are 
implemented with write-once attributes, and they are only used by firmware and 
reserved for OS.   In addition,  with this change,  it can benefit all VMMs 
(not just Xen) which use Qemu as device model.  If adopt xenstore way, perhaps 
other VMMs also have to write similar and duplicate logic for the same purpose. 
 
Xiantao 


> On Tue, 2013-02-26 at 15:43 +0000, Stefano Stabellini wrote:
> > 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: qemu-devel-bounces+xiantao.zhang=intel.com@xxxxxxxxxx
> > > > [mailto:qemu-devel-bounces+xiantao.zhang=intel.com@xxxxxxxxxx] On
> Behalf
> > > > Of Hao, Xudong
> > > > Sent: Tuesday, February 26, 2013 11:33 AM
> > > > To: Stefano Stabellini; Ian Campbell
> > > > Cc: aliguori@xxxxxxxxxx; mst@xxxxxxxxxx; qemu-devel@xxxxxxxxxx;
> xen-
> > > > devel@xxxxxxxxxxxxx; JBeulich@xxxxxxxx; afaerber@xxxxxxx
> > > > Subject: Re: [Qemu-devel] [PATCH v2] piix: define a TOM register to
> report the
> > > > base of PCI
> > > >
> > > > > -----Original Message-----
> > > > > From: qemu-devel-bounces+xudong.hao=intel.com@xxxxxxxxxx
> > > > > [mailto:qemu-devel-bounces+xudong.hao=intel.com@xxxxxxxxxx] On
> Behalf
> > > > > Of Stefano Stabellini
> > > > > Sent: Tuesday, February 26, 2013 12:06 AM
> > > > > To: Hao, Xudong
> > > > > Cc: aliguori@xxxxxxxxxx; Stefano Stabellini; mst@xxxxxxxxxx;
> > > > > qemu-devel@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxx; JBeulich@xxxxxxxx;
> > > > > afaerber@xxxxxxx
> > > > > 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 <xudong.hao@xxxxxxxxx>
> > > > > > Signed-off-by: Xiantao Zhang <xiantao.zhang@xxxxxxxxx>
> > > > >
> > > > > 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
> > > > > >
> > > >
> > >
> 

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