diff mbox series

[V7,03/11] vpci/header: implement guest BAR register handlers

Message ID 20220719174253.541965-4-olekstysh@gmail.com (mailing list archive)
State New, archived
Headers show
Series PCI devices passthrough on Arm, part 3 | expand

Commit Message

Oleksandr Tyshchenko July 19, 2022, 5:42 p.m. UTC 
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Add relevant vpci register handlers when assigning PCI device to a domain
and remove those when de-assigning. This allows having different
handlers for different domains, e.g. hwdom and other guests.

Emulate guest BAR register values: this allows creating a guest view
of the registers and emulates size and properties probe as it is done
during PCI device enumeration by the guest.

All empty, IO and ROM BARs for guests are emulated by returning 0 on
reads and ignoring writes: this BARs are special with this respect as
their lower bits have special meaning, so returning default ~0 on read
may confuse guest OS.

Memory decoding is initially disabled when used by guests in order to
prevent the BAR being placed on top of a RAM region.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
Since v6:
- unify the writing of the PCI_COMMAND register on the
  error path into a label
- do not introduce bar_ignore_access helper and open code
- s/guest_bar_ignore_read/empty_bar_read
- update error message in guest_bar_write
- only setup empty_bar_read for IO if !x86
- OT: rebased
- OT: add cf_check specifier to guest_bar_(write)read() and empty_bar_read()
Since v5:
- make sure that the guest set address has the same page offset
  as the physical address on the host
- remove guest_rom_{read|write} as those just implement the default
  behaviour of the registers not being handled
- adjusted comment for struct vpci.addr field
- add guest handlers for BARs which are not handled and will otherwise
  return ~0 on read and ignore writes. The BARs are special with this
  respect as their lower bits have special meaning, so returning ~0
  doesn't seem to be right
Since v4:
- updated commit message
- s/guest_addr/guest_reg
Since v3:
- squashed two patches: dynamic add/remove handlers and guest BAR
  handler implementation
- fix guest BAR read of the high part of a 64bit BAR (Roger)
- add error handling to vpci_assign_device
- s/dom%pd/%pd
- blank line before return
Since v2:
- remove unneeded ifdefs for CONFIG_HAS_VPCI_GUEST_SUPPORT as more code
  has been eliminated from being built on x86
Since v1:
 - constify struct pci_dev where possible
 - do not open code is_system_domain()
 - simplify some code3. simplify
 - use gdprintk + error code instead of gprintk
 - gate vpci_bar_{add|remove}_handlers with CONFIG_HAS_VPCI_GUEST_SUPPORT,
   so these do not get compiled for x86
 - removed unneeded is_system_domain check
 - re-work guest read/write to be much simpler and do more work on write
   than read which is expected to be called more frequently
 - removed one too obvious comment
---
 xen/drivers/vpci/header.c | 151 +++++++++++++++++++++++++++++++-------
 xen/include/xen/vpci.h    |   3 +
 2 files changed, 126 insertions(+), 28 deletions(-)

Comments

Jan Beulich July 27, 2022, 10:15 a.m. UTC | #1 
On 19.07.2022 19:42, Oleksandr Tyshchenko wrote:
> @@ -527,6 +592,17 @@ static int cf_check init_bars(struct pci_dev *pdev)
>          if ( (val & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO )
>          {
>              bars[i].type = VPCI_BAR_IO;
> +
> +#ifndef CONFIG_X86
> +            if ( !is_hwdom )
> +            {
> +                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
> +                                       reg, 4, &bars[i]);
> +                if ( rc )
> +                    goto fail;
> +            }
> +#endif

Since long term this can't be correct, it wants a TODO comment put next
to it.

> @@ -553,34 +635,47 @@ static int cf_check init_bars(struct pci_dev *pdev)
>          bars[i].size = size;
>          bars[i].prefetchable = val & PCI_BASE_ADDRESS_MEM_PREFETCH;
>  
> -        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, bar_write, reg, 4,
> -                               &bars[i]);
> +        rc = vpci_add_register(pdev->vpci,
> +                               is_hwdom ? vpci_hw_read32 : guest_bar_read,
> +                               is_hwdom ? bar_write : guest_bar_write,
> +                               reg, 4, &bars[i]);
>          if ( rc )
> -        {
> -            pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
> -            return rc;
> -        }
> +            goto fail;
>      }
>  
> -    /* Check expansion ROM. */
> -    rc = pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM);
> -    if ( rc > 0 && size )
> +    /* Check expansion ROM: we do not handle ROM for guests. */
> +    if ( is_hwdom )

This again can't be right long-term. Personally I'd prefer if the code
was (largely) left as is, with adjustments (with suitable TODO comments)
made on a much smaller scope only. But I'm not the maintainer of this
code - Roger may have a different view on this.

Jan
Oleksandr Tyshchenko July 27, 2022, 4:17 p.m. UTC | #2 
On 27.07.22 13:15, Jan Beulich wrote:

Hello Jan

> On 19.07.2022 19:42, Oleksandr Tyshchenko wrote:
>> @@ -527,6 +592,17 @@ static int cf_check init_bars(struct pci_dev *pdev)
>>           if ( (val & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO )
>>           {
>>               bars[i].type = VPCI_BAR_IO;
>> +
>> +#ifndef CONFIG_X86
>> +            if ( !is_hwdom )
>> +            {
>> +                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
>> +                                       reg, 4, &bars[i]);
>> +                if ( rc )
>> +                    goto fail;
>> +            }
>> +#endif
> Since long term this can't be correct, it wants a TODO comment put next
> to it.


Looking into the previous versions of this patch (up to V3) I failed to 
find any changes in current version which hadn't been discussed (and 
agreed in some form).

Could you please clarify what exactly can't be correct the long term, 
for me to put the proper TODO here. Do you perhaps mean that TODO needs 
to explain why we have to diverge?


>
>> @@ -553,34 +635,47 @@ static int cf_check init_bars(struct pci_dev *pdev)
>>           bars[i].size = size;
>>           bars[i].prefetchable = val & PCI_BASE_ADDRESS_MEM_PREFETCH;
>>   
>> -        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, bar_write, reg, 4,
>> -                               &bars[i]);
>> +        rc = vpci_add_register(pdev->vpci,
>> +                               is_hwdom ? vpci_hw_read32 : guest_bar_read,
>> +                               is_hwdom ? bar_write : guest_bar_write,
>> +                               reg, 4, &bars[i]);
>>           if ( rc )
>> -        {
>> -            pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
>> -            return rc;
>> -        }
>> +            goto fail;
>>       }
>>   
>> -    /* Check expansion ROM. */
>> -    rc = pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM);
>> -    if ( rc > 0 && size )
>> +    /* Check expansion ROM: we do not handle ROM for guests. */
>> +    if ( is_hwdom )
> This again can't be right long-term. Personally I'd prefer if the code
> was (largely) left as is, with adjustments (with suitable TODO comments)
> made on a much smaller scope only.


I can revive a comment that Oleksandr Andrushchenko provided for earlier 
version by transforming into TODO:


ROM BAR is only handled for the hardware domain and for guest domains
there is a stub: at the moment PCI expansion ROM handling is supported
for x86 only and it might not be used by other architectures without
emulating x86. Other use-cases may include using that expansion ROM before
Xen boots, hence no emulation is needed in Xen itself. Or when a guest
wants to use the ROM code which seems to be rare.



>   But I'm not the maintainer of this
> code - Roger may have a different view on this.


Well, let's wait for Roger's input here.


>
> Jan
Jan Beulich July 28, 2022, 7:01 a.m. UTC | #3 
On 27.07.2022 18:17, Oleksandr wrote:
> On 27.07.22 13:15, Jan Beulich wrote:
>> On 19.07.2022 19:42, Oleksandr Tyshchenko wrote:
>>> @@ -527,6 +592,17 @@ static int cf_check init_bars(struct pci_dev *pdev)
>>>           if ( (val & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO )
>>>           {
>>>               bars[i].type = VPCI_BAR_IO;
>>> +
>>> +#ifndef CONFIG_X86
>>> +            if ( !is_hwdom )
>>> +            {
>>> +                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
>>> +                                       reg, 4, &bars[i]);
>>> +                if ( rc )
>>> +                    goto fail;
>>> +            }
>>> +#endif
>> Since long term this can't be correct, it wants a TODO comment put next
>> to it.
> 
> 
> Looking into the previous versions of this patch (up to V3) I failed to 
> find any changes in current version which hadn't been discussed (and 
> agreed in some form).
> 
> Could you please clarify what exactly can't be correct the long term, 
> for me to put the proper TODO here. Do you perhaps mean that TODO needs 
> to explain why we have to diverge?

If a device has I/O port ranges, then that's typically for a reason.
Drivers (in the guest) may therefore want to use those ranges to
communicate with the device. Imagine in particular a device without
any MMIO BARs, and with only I/O port one(s).

>>> @@ -553,34 +635,47 @@ static int cf_check init_bars(struct pci_dev *pdev)
>>>           bars[i].size = size;
>>>           bars[i].prefetchable = val & PCI_BASE_ADDRESS_MEM_PREFETCH;
>>>   
>>> -        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, bar_write, reg, 4,
>>> -                               &bars[i]);
>>> +        rc = vpci_add_register(pdev->vpci,
>>> +                               is_hwdom ? vpci_hw_read32 : guest_bar_read,
>>> +                               is_hwdom ? bar_write : guest_bar_write,
>>> +                               reg, 4, &bars[i]);
>>>           if ( rc )
>>> -        {
>>> -            pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
>>> -            return rc;
>>> -        }
>>> +            goto fail;
>>>       }
>>>   
>>> -    /* Check expansion ROM. */
>>> -    rc = pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM);
>>> -    if ( rc > 0 && size )
>>> +    /* Check expansion ROM: we do not handle ROM for guests. */
>>> +    if ( is_hwdom )
>> This again can't be right long-term. Personally I'd prefer if the code
>> was (largely) left as is, with adjustments (with suitable TODO comments)
>> made on a much smaller scope only.
> 
> 
> I can revive a comment that Oleksandr Andrushchenko provided for earlier 
> version by transforming into TODO:
> 
> 
> ROM BAR is only handled for the hardware domain and for guest domains
> there is a stub: at the moment PCI expansion ROM handling is supported
> for x86 only and it might not be used by other architectures without
> emulating x86. Other use-cases may include using that expansion ROM before
> Xen boots, hence no emulation is needed in Xen itself. Or when a guest
> wants to use the ROM code which seems to be rare.

ROMs can contain other than x86 code. While reportedly mostly dead, EFI
bytecode was an example of an abstraction layer supporting arbitrary
architectures. Therefore a comment along these lines would be okay, but
personally I'd prefer it to be less verbose - along the lines of the
one to be supplied for the I/O port restriction.

Jan
Oleksandr Tyshchenko July 28, 2022, 2:56 p.m. UTC | #4 
On 28.07.22 10:01, Jan Beulich wrote:

Hello Jan


> On 27.07.2022 18:17, Oleksandr wrote:
>> On 27.07.22 13:15, Jan Beulich wrote:
>>> On 19.07.2022 19:42, Oleksandr Tyshchenko wrote:
>>>> @@ -527,6 +592,17 @@ static int cf_check init_bars(struct pci_dev *pdev)
>>>>            if ( (val & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO )
>>>>            {
>>>>                bars[i].type = VPCI_BAR_IO;
>>>> +
>>>> +#ifndef CONFIG_X86
>>>> +            if ( !is_hwdom )
>>>> +            {
>>>> +                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
>>>> +                                       reg, 4, &bars[i]);
>>>> +                if ( rc )
>>>> +                    goto fail;
>>>> +            }
>>>> +#endif
>>> Since long term this can't be correct, it wants a TODO comment put next
>>> to it.
>>
>> Looking into the previous versions of this patch (up to V3) I failed to
>> find any changes in current version which hadn't been discussed (and
>> agreed in some form).
>>
>> Could you please clarify what exactly can't be correct the long term,
>> for me to put the proper TODO here. Do you perhaps mean that TODO needs
>> to explain why we have to diverge?
> If a device has I/O port ranges, then that's typically for a reason.
> Drivers (in the guest) may therefore want to use those ranges to
> communicate with the device. Imagine in particular a device without
> any MMIO BARs, and with only I/O port one(s).
>
>>>> @@ -553,34 +635,47 @@ static int cf_check init_bars(struct pci_dev *pdev)
>>>>            bars[i].size = size;
>>>>            bars[i].prefetchable = val & PCI_BASE_ADDRESS_MEM_PREFETCH;
>>>>    
>>>> -        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, bar_write, reg, 4,
>>>> -                               &bars[i]);
>>>> +        rc = vpci_add_register(pdev->vpci,
>>>> +                               is_hwdom ? vpci_hw_read32 : guest_bar_read,
>>>> +                               is_hwdom ? bar_write : guest_bar_write,
>>>> +                               reg, 4, &bars[i]);
>>>>            if ( rc )
>>>> -        {
>>>> -            pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
>>>> -            return rc;
>>>> -        }
>>>> +            goto fail;
>>>>        }
>>>>    
>>>> -    /* Check expansion ROM. */
>>>> -    rc = pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM);
>>>> -    if ( rc > 0 && size )
>>>> +    /* Check expansion ROM: we do not handle ROM for guests. */
>>>> +    if ( is_hwdom )
>>> This again can't be right long-term. Personally I'd prefer if the code
>>> was (largely) left as is, with adjustments (with suitable TODO comments)
>>> made on a much smaller scope only.
>>
>> I can revive a comment that Oleksandr Andrushchenko provided for earlier
>> version by transforming into TODO:
>>
>>
>> ROM BAR is only handled for the hardware domain and for guest domains
>> there is a stub: at the moment PCI expansion ROM handling is supported
>> for x86 only and it might not be used by other architectures without
>> emulating x86. Other use-cases may include using that expansion ROM before
>> Xen boots, hence no emulation is needed in Xen itself. Or when a guest
>> wants to use the ROM code which seems to be rare.
> ROMs can contain other than x86 code. While reportedly mostly dead, EFI
> bytecode was an example of an abstraction layer supporting arbitrary
> architectures. Therefore a comment along these lines would be okay, but
> personally I'd prefer it to be less verbose - along the lines of the
> one to be supplied for the I/O port restriction.


Thanks for the clarification. I will add two TODOs.



>
> Jan
diff mbox series

Patch

diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index e0461b1139..9fbbdc3500 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -412,6 +412,71 @@  static void cf_check bar_write(
     pci_conf_write32(pdev->sbdf, reg, val);
 }
 
+static void cf_check guest_bar_write(
+    const struct pci_dev *pdev, unsigned int reg, uint32_t val, void *data)
+{
+    struct vpci_bar *bar = data;
+    bool hi = false;
+    uint64_t guest_reg = bar->guest_reg;
+
+    if ( bar->type == VPCI_BAR_MEM64_HI )
+    {
+        ASSERT(reg > PCI_BASE_ADDRESS_0);
+        bar--;
+        hi = true;
+    }
+    else
+    {
+        val &= PCI_BASE_ADDRESS_MEM_MASK;
+        val |= bar->type == VPCI_BAR_MEM32 ? PCI_BASE_ADDRESS_MEM_TYPE_32
+                                           : PCI_BASE_ADDRESS_MEM_TYPE_64;
+        val |= bar->prefetchable ? PCI_BASE_ADDRESS_MEM_PREFETCH : 0;
+    }
+
+    guest_reg &= ~(0xffffffffull << (hi ? 32 : 0));
+    guest_reg |= (uint64_t)val << (hi ? 32 : 0);
+
+    guest_reg &= ~(bar->size - 1) | ~PCI_BASE_ADDRESS_MEM_MASK;
+
+    /*
+     * Make sure that the guest set address has the same page offset
+     * as the physical address on the host or otherwise things won't work as
+     * expected.
+     */
+    if ( (guest_reg & (~PAGE_MASK & PCI_BASE_ADDRESS_MEM_MASK)) !=
+         (bar->addr & ~PAGE_MASK) )
+    {
+        gprintk(XENLOG_WARNING,
+                "%pp: ignored BAR %zu write attempting to change page offset\n",
+                &pdev->sbdf, bar - pdev->vpci->header.bars + hi);
+        return;
+    }
+
+    bar->guest_reg = guest_reg;
+}
+
+static uint32_t cf_check guest_bar_read(
+    const struct pci_dev *pdev, unsigned int reg, void *data)
+{
+    const struct vpci_bar *bar = data;
+    bool hi = false;
+
+    if ( bar->type == VPCI_BAR_MEM64_HI )
+    {
+        ASSERT(reg > PCI_BASE_ADDRESS_0);
+        bar--;
+        hi = true;
+    }
+
+    return bar->guest_reg >> (hi ? 32 : 0);
+}
+
+static uint32_t cf_check empty_bar_read(
+    const struct pci_dev *pdev, unsigned int reg, void *data)
+{
+    return 0;
+}
+
 static void cf_check rom_write(
     const struct pci_dev *pdev, unsigned int reg, uint32_t val, void *data)
 {
@@ -468,6 +533,7 @@  static int cf_check init_bars(struct pci_dev *pdev)
     struct vpci_header *header;
     struct vpci_bar *bars;
     int rc;
+    bool is_hwdom = is_hardware_domain(pdev->domain);
 
     ASSERT(pcidevs_write_locked());
 
@@ -512,13 +578,12 @@  static int cf_check init_bars(struct pci_dev *pdev)
         if ( i && bars[i - 1].type == VPCI_BAR_MEM64_LO )
         {
             bars[i].type = VPCI_BAR_MEM64_HI;
-            rc = vpci_add_register(pdev->vpci, vpci_hw_read32, bar_write, reg,
-                                   4, &bars[i]);
+            rc = vpci_add_register(pdev->vpci,
+                                   is_hwdom ? vpci_hw_read32 : guest_bar_read,
+                                   is_hwdom ? bar_write : guest_bar_write,
+                                   reg, 4, &bars[i]);
             if ( rc )
-            {
-                pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
-                return rc;
-            }
+                goto fail;
 
             continue;
         }
@@ -527,6 +592,17 @@  static int cf_check init_bars(struct pci_dev *pdev)
         if ( (val & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO )
         {
             bars[i].type = VPCI_BAR_IO;
+
+#ifndef CONFIG_X86
+            if ( !is_hwdom )
+            {
+                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
+                                       reg, 4, &bars[i]);
+                if ( rc )
+                    goto fail;
+            }
+#endif
+
             continue;
         }
         if ( (val & PCI_BASE_ADDRESS_MEM_TYPE_MASK) ==
@@ -538,14 +614,20 @@  static int cf_check init_bars(struct pci_dev *pdev)
         rc = pci_size_mem_bar(pdev->sbdf, reg, &addr, &size,
                               (i == num_bars - 1) ? PCI_BAR_LAST : 0);
         if ( rc < 0 )
-        {
-            pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
-            return rc;
-        }
+            goto fail;
 
         if ( size == 0 )
         {
             bars[i].type = VPCI_BAR_EMPTY;
+
+            if ( !is_hwdom )
+            {
+                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
+                                       reg, 4, &bars[i]);
+                if ( rc )
+                    goto fail;
+            }
+
             continue;
         }
 
@@ -553,34 +635,47 @@  static int cf_check init_bars(struct pci_dev *pdev)
         bars[i].size = size;
         bars[i].prefetchable = val & PCI_BASE_ADDRESS_MEM_PREFETCH;
 
-        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, bar_write, reg, 4,
-                               &bars[i]);
+        rc = vpci_add_register(pdev->vpci,
+                               is_hwdom ? vpci_hw_read32 : guest_bar_read,
+                               is_hwdom ? bar_write : guest_bar_write,
+                               reg, 4, &bars[i]);
         if ( rc )
-        {
-            pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
-            return rc;
-        }
+            goto fail;
     }
 
-    /* Check expansion ROM. */
-    rc = pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM);
-    if ( rc > 0 && size )
+    /* Check expansion ROM: we do not handle ROM for guests. */
+    if ( is_hwdom )
     {
-        struct vpci_bar *rom = &header->bars[num_bars];
+        rc = pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM);
+        if ( rc > 0 && size )
+        {
+            struct vpci_bar *rom = &header->bars[num_bars];
 
-        rom->type = VPCI_BAR_ROM;
-        rom->size = size;
-        rom->addr = addr;
-        header->rom_enabled = pci_conf_read32(pdev->sbdf, rom_reg) &
-                              PCI_ROM_ADDRESS_ENABLE;
+            rom->type = VPCI_BAR_ROM;
+            rom->size = size;
+            rom->addr = addr;
+            header->rom_enabled = pci_conf_read32(pdev->sbdf, rom_reg) &
+                                  PCI_ROM_ADDRESS_ENABLE;
 
-        rc = vpci_add_register(pdev->vpci, vpci_hw_read32, rom_write, rom_reg,
-                               4, rom);
+            rc = vpci_add_register(pdev->vpci, vpci_hw_read32, rom_write,
+                                   rom_reg, 4, rom);
+            if ( rc )
+                rom->type = VPCI_BAR_EMPTY;
+        }
+    }
+    else
+    {
+        rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
+                               rom_reg, 4, &header->bars[num_bars]);
         if ( rc )
-            rom->type = VPCI_BAR_EMPTY;
+            goto fail;
     }
 
     return (cmd & PCI_COMMAND_MEMORY) ? modify_bars(pdev, cmd, false) : 0;
+
+ fail:
+    pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
+    return rc;
 }
 REGISTER_VPCI_INIT(init_bars, VPCI_PRIORITY_MIDDLE);
 
diff --git a/xen/include/xen/vpci.h b/xen/include/xen/vpci.h
index e5501b9207..6e1d3b93cd 100644
--- a/xen/include/xen/vpci.h
+++ b/xen/include/xen/vpci.h
@@ -67,7 +67,10 @@  struct vpci {
     struct vpci_header {
         /* Information about the PCI BARs of this device. */
         struct vpci_bar {
+            /* Physical (host) address. */
             uint64_t addr;
+            /* Guest view of the BAR: address and lower bits. */
+            uint64_t guest_reg;
             uint64_t size;
             enum {
                 VPCI_BAR_EMPTY,