Re: [PATCH v11 07/17] vpci/header: implement guest BAR register handlers

["Roger Pau Monné" <roger.pau@citrix.com>]

On Sat, Dec 02, 2023 at 01:27:04AM +0000, Volodymyr Babchuk wrote:
> 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.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>

Just a couple of nits.

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

> ---
> In v11:
> - Access guest_addr after adjusting for MEM64_HI bar in
> guest_bar_write()
> - guest bar handlers renamed and now  _mem_ part to denote
> that they are handling only memory BARs
> - refuse to update guest BAR address if BAR is enabled
> In v10:
> - ull -> ULL to be MISRA-compatbile
> - Use PAGE_OFFSET() instead of combining with ~PAGE_MASK
> - Set type of empty bars to VPCI_BAR_EMPTY
> In v9:
> - factored-out "fail" label introduction in init_bars()
> - replaced #ifdef CONFIG_X86 with IS_ENABLED()
> - do not pass bars[i] to empty_bar_read() handler
> - store guest's BAR address instead of guests BAR register view
> 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
> 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 | 135 +++++++++++++++++++++++++++++++++-----
>  xen/include/xen/vpci.h    |   3 +
>  2 files changed, 122 insertions(+), 16 deletions(-)
> 
> diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
> index e6a1d58c42..43216429d9 100644
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -477,6 +477,75 @@ static void cf_check bar_write(
>      pci_conf_write32(pdev->sbdf, reg, val);
>  }
>  
> +static void cf_check guest_mem_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_addr;
> +
> +    if ( bar->type == VPCI_BAR_MEM64_HI )
> +    {
> +        ASSERT(reg > PCI_BASE_ADDRESS_0);
> +        bar--;
> +        hi = true;
> +    }
> +    else
> +    {
> +        val &= PCI_BASE_ADDRESS_MEM_MASK;
> +    }
> +
> +    guest_addr = bar->guest_addr;
> +    guest_addr &= ~(0xffffffffULL << (hi ? 32 : 0));
> +    guest_addr |= (uint64_t)val << (hi ? 32 : 0);
> +
> +    /* Allow guest to size BAR correctly */
> +    guest_addr &= ~(bar->size - 1);
> +
> +    /*
> +     * Xen only cares whether the BAR is mapped into the p2m, so allow BAR
> +     * writes as long as the BAR is not mapped into the p2m.
> +     */
> +    if ( bar->enabled )
> +    {
> +        /* If the value written is the current one avoid printing a warning. */
> +        if ( guest_addr != bar->guest_addr )
> +            gprintk(XENLOG_WARNING,
> +                    "%pp: ignored guest BAR %zu write while mapped\n",
> +                    &pdev->sbdf, bar - pdev->vpci->header.bars + hi);
> +        return;
> +    }
> +    bar->guest_addr = guest_addr;
> +}
> +
> +static uint32_t cf_check guest_mem_bar_read(const struct pci_dev *pdev,
> +                                            unsigned int reg, void *data)
> +{
> +    const struct vpci_bar *bar = data;
> +    uint32_t reg_val;
> +
> +    if ( bar->type == VPCI_BAR_MEM64_HI )
> +    {
> +        ASSERT(reg > PCI_BASE_ADDRESS_0);
> +        bar--;
> +        return bar->guest_addr >> 32;
> +    }
> +
> +    reg_val = bar->guest_addr;
> +    reg_val |= bar->type == VPCI_BAR_MEM32 ? PCI_BASE_ADDRESS_MEM_TYPE_32 :
> +                                             PCI_BASE_ADDRESS_MEM_TYPE_64;
> +    reg_val |= bar->prefetchable ? PCI_BASE_ADDRESS_MEM_PREFETCH : 0;
> +
> +    return reg_val;
> +}
> +
> +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)
>  {
> @@ -537,6 +606,7 @@ static int cf_check init_bars(struct pci_dev *pdev)
>      struct vpci_header *header = &pdev->vpci->header;
>      struct vpci_bar *bars = header->bars;
>      int rc;
> +    bool is_hwdom = is_hardware_domain(pdev->domain);
>  
>      ASSERT(rw_is_write_locked(&pdev->domain->pci_lock));
>  
> @@ -578,8 +648,11 @@ 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_mem_bar_read,

Nit: I would usually indent this as:

is_hwdom ? vpci_hw_read32
         : guest_mem_bar_read,

> +                                   is_hwdom ? bar_write : guest_mem_bar_write,
> +                                   reg, 4, &bars[i]);
>              if ( rc )
>                  goto fail;
>  
> @@ -590,6 +663,14 @@ 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;
> +            if ( !IS_ENABLED(CONFIG_X86) && !is_hwdom )
> +            {
> +                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
> +                                       reg, 4, NULL);
> +                if ( rc )
> +                    goto fail;
> +            }
> +
>              continue;
>          }
>          if ( (val & PCI_BASE_ADDRESS_MEM_TYPE_MASK) ==
> @@ -606,6 +687,15 @@ static int cf_check init_bars(struct pci_dev *pdev)
>          if ( size == 0 )
>          {
>              bars[i].type = VPCI_BAR_EMPTY;
> +
> +            if ( !is_hwdom )
> +            {
> +                rc = vpci_add_register(pdev->vpci, empty_bar_read, NULL,
> +                                       reg, 4, NULL);
> +                if ( rc )
> +                    goto fail;
> +            }
> +
>              continue;
>          }
>  
> @@ -613,28 +703,41 @@ 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_mem_bar_read,
> +                               is_hwdom ? bar_write : guest_mem_bar_write,
> +                               reg, 4, &bars[i]);
>          if ( rc )
>              goto fail;
>      }
>  
> -    /* Check expansion ROM. */
> -    rc = pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM);

Nit: I guess you could do something like:

rc = is_hwdom ? pci_size_mem_bar(pdev->sbdf, rom_reg, &addr, &size, PCI_BAR_ROM)
              : 0;

And that would avoid having to re-indent the whole block?

You could still place the domU code on an else ( !is_hwdom ) branch.

Overall I'm not sure what I prefer, as the re-indentation would be
better done in a non-functional change IMO.

Thanks, Roger.