Re: [PATCH v2 2/3] vpci: allow BAR map/unmap without affecting memory decoding bit

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jul 23, 2025 at 12:37:42PM -0400, Stewart Hildebrand wrote:
> Introduce enum vpci_map_op and allow invoking modify_bars() without
> changing the memory decoding bit.
> 
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
> ---
> v1->v2:
> * new patch
> ---
>  xen/drivers/vpci/header.c | 22 +++++++++++++++-------
>  xen/include/xen/vpci.h    |  4 ++++
>  2 files changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
> index df065a5f5faf..1c66796b625b 100644
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -189,7 +189,7 @@ static bool vpci_process_map_task(struct vpci_map_task 
> *task)
>          struct vpci_bar_map *bar = &task->bars[i];
>          struct map_data data = {
>              .d = task->domain,
> -            .map = task->cmd & PCI_COMMAND_MEMORY,
> +            .map = task->map_op == VPCI_MAP,
>              .bar = bar,
>          };
>          int rc;
> @@ -298,7 +298,9 @@ static int __init apply_map(struct vpci_map_task *task)
>  }
>  
>  static struct vpci_map_task *alloc_map_task(const struct pci_dev *pdev,
> -                                            uint16_t cmd, bool rom_only)
> +                                            uint16_t cmd,
> +                                            enum vpci_map_op map_op,
> +                                            bool rom_only)
>  {
>      struct vpci_map_task *task = xzalloc(struct vpci_map_task);
>      unsigned int i;
> @@ -333,6 +335,7 @@ static struct vpci_map_task *alloc_map_task(const struct 
> pci_dev *pdev,
>      task->pdev = pdev;
>      task->domain = pdev->domain;
>      task->cmd = cmd;
> +    task->map_op = map_op;
>      task->rom_only = rom_only;
>  
>      return task;
> @@ -359,13 +362,14 @@ static void defer_map(struct vpci_map_task *task)
>      raise_softirq(SCHEDULE_SOFTIRQ);
>  }
>  
> -static int modify_bars(const struct pci_dev *pdev, uint16_t cmd, bool 
> rom_only)
> +static int modify_bars(const struct pci_dev *pdev, uint16_t cmd,
> +                       enum vpci_map_op map_op, bool rom_only)
>  {
>      struct vpci_header *header = &pdev->vpci->header;
>      struct pci_dev *tmp;
>      const struct domain *d;
>      const struct vpci_msix *msix = pdev->vpci->msix;
> -    struct vpci_map_task *task = alloc_map_task(pdev, cmd, rom_only);
> +    struct vpci_map_task *task = alloc_map_task(pdev, cmd, map_op, rom_only);
>      unsigned int i, j;
>      int rc;
>  
> @@ -614,7 +618,8 @@ static void cf_check cmd_write(
>           * memory decoding bit has not been changed, so leave everything 
> as-is,
>           * hoping the guest will realize and try again.
>           */
> -        modify_bars(pdev, cmd, false);
> +        modify_bars(pdev, cmd, cmd & PCI_COMMAND_MEMORY ? VPCI_MAP : 
> VPCI_UNMAP,
> +                    false);
>      else
>          pci_conf_write16(pdev->sbdf, reg, cmd);
>  }
> @@ -782,7 +787,8 @@ static void cf_check rom_write(
>       * Pass PCI_COMMAND_MEMORY or 0 to signal a map/unmap request, note that
>       * this fabricated command is never going to be written to the register.
>       */
> -    else if ( modify_bars(pdev, new_enabled ? PCI_COMMAND_MEMORY : 0, true) )
> +    else if ( modify_bars(pdev, new_enabled ? PCI_COMMAND_MEMORY : 0,
> +                          new_enabled ? VPCI_MAP : VPCI_UNMAP, true) )
>          /*
>           * No memory has been added or removed from the p2m (because the 
> actual
>           * p2m changes are deferred in defer_map) and the ROM enable bit has
> @@ -1067,7 +1073,9 @@ static int cf_check init_header(struct pci_dev *pdev)
>              goto fail;
>      }
>  
> -    return (cmd & PCI_COMMAND_MEMORY) ? modify_bars(pdev, cmd, false) : 0;
> +    return (cmd & PCI_COMMAND_MEMORY)
> +           ? modify_bars(pdev, cmd, VPCI_MAP, false)
> +           : 0;
>  
>   fail:
>      pci_conf_write16(pdev->sbdf, PCI_COMMAND, cmd);
> diff --git a/xen/include/xen/vpci.h b/xen/include/xen/vpci.h
> index c2e75076691f..fb6cad62d418 100644
> --- a/xen/include/xen/vpci.h
> +++ b/xen/include/xen/vpci.h
> @@ -205,6 +205,10 @@ struct vpci_map_task {
>          struct rangeset *mem;
>      } bars[PCI_HEADER_NORMAL_NR_BARS + 1];
>      uint16_t cmd;
> +    enum vpci_map_op {
> +        VPCI_MAP,
> +        VPCI_UNMAP,
> +    } map_op;
>      bool rom_only : 1;

Since you already have a bitfield here, I would consider using a
boolean also, ie:

bool rom_only : 1;
bool map : 1;

Or are we expecting to gain new operations aside from map and unmap?

Thanks, Roger.