Re: [PATCH v4 11/15] pci: Add pci_iomap_shared{,_range}

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Aug 04, 2021 at 05:52:14PM -0700, Kuppuswamy Sathyanarayanan wrote:
> From: Andi Kleen <ak@linux.intel.com>
> 
> Add a new variant of pci_iomap for mapping all PCI resources
> of a devices as shared memory with a hypervisor in a confidential
> guest.
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

I'm a bit puzzled by this part. So why should the guest *not* map
pci memory as shared? And if the answer is never (as it seems to be)
then why not just make regular pci_iomap DTRT?

Thanks!

> ---
>  include/asm-generic/pci_iomap.h |  6 +++++
>  lib/pci_iomap.c                 | 46 +++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/include/asm-generic/pci_iomap.h b/include/asm-generic/pci_iomap.h
> index d4f16dcc2ed7..0178ddd7ad88 100644
> --- a/include/asm-generic/pci_iomap.h
> +++ b/include/asm-generic/pci_iomap.h
> @@ -18,6 +18,12 @@ extern void __iomem *pci_iomap_range(struct pci_dev *dev, int bar,
>  extern void __iomem *pci_iomap_wc_range(struct pci_dev *dev, int bar,
>  					unsigned long offset,
>  					unsigned long maxlen);
> +extern void __iomem *pci_iomap_shared(struct pci_dev *dev, int bar,
> +				      unsigned long max);
> +extern void __iomem *pci_iomap_shared_range(struct pci_dev *dev, int bar,
> +					    unsigned long offset,
> +					    unsigned long maxlen);
> +
>  /* Create a virtual mapping cookie for a port on a given PCI device.
>   * Do not call this directly, it exists to make it easier for architectures
>   * to override */
> diff --git a/lib/pci_iomap.c b/lib/pci_iomap.c
> index 6251c3f651c6..b04e8689eab3 100644
> --- a/lib/pci_iomap.c
> +++ b/lib/pci_iomap.c
> @@ -25,6 +25,11 @@ static void __iomem *map_ioremap_wc(phys_addr_t addr, size_t size)
>  	return ioremap_wc(addr, size);
>  }
>  
> +static void __iomem *map_ioremap_shared(phys_addr_t addr, size_t size)
> +{
> +	return ioremap_shared(addr, size);
> +}
> +
>  static void __iomem *pci_iomap_range_map(struct pci_dev *dev,
>  					 int bar,
>  					 unsigned long offset,
> @@ -101,6 +106,47 @@ void __iomem *pci_iomap_wc_range(struct pci_dev *dev,
>  }
>  EXPORT_SYMBOL_GPL(pci_iomap_wc_range);
>  
> +/**
> + * pci_iomap_shared_range - create a virtual shared mapping cookie for a
> + *                          PCI BAR
> + * @dev: PCI device that owns the BAR
> + * @bar: BAR number
> + * @offset: map memory at the given offset in BAR
> + * @maxlen: max length of the memory to map
> + *
> + * Remap a pci device's resources shared in a confidential guest.
> + * For more details see pci_iomap_range's documentation.
> + *
> + * @maxlen specifies the maximum length to map. To get access to
> + * the complete BAR from offset to the end, pass %0 here.
> + */
> +void __iomem *pci_iomap_shared_range(struct pci_dev *dev, int bar,
> +				     unsigned long offset, unsigned long maxlen)
> +{
> +	return pci_iomap_range_map(dev, bar, offset, maxlen,
> +				   map_ioremap_shared);
> +}
> +EXPORT_SYMBOL_GPL(pci_iomap_shared_range);
> +
> +/**
> + * pci_iomap_shared - create a virtual shared mapping cookie for a PCI BAR
> + * @dev: PCI device that owns the BAR
> + * @bar: BAR number
> + * @maxlen: length of the memory to map
> + *
> + * See pci_iomap for details. This function creates a shared mapping
> + * with the host for confidential hosts.
> + *
> + * @maxlen specifies the maximum length to map. To get access to the
> + * complete BAR without checking for its length first, pass %0 here.
> + */
> +void __iomem *pci_iomap_shared(struct pci_dev *dev, int bar,
> +			       unsigned long maxlen)
> +{
> +	return pci_iomap_shared_range(dev, bar, 0, maxlen);
> +}
> +EXPORT_SYMBOL_GPL(pci_iomap_shared);
> +
>  /**
>   * pci_iomap - create a virtual mapping cookie for a PCI BAR
>   * @dev: PCI device that owns the BAR
> -- 
> 2.25.1