Re: [PATCH 2/2] x86/pci: Treat EfiMemoryMappedIO as reservation of ECAM space

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, January 10, 2023 7:02:43 PM CET Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> Normally we reject ECAM space unless it is reported as reserved in the E820
> table or via a PNP0C02 _CRS method (PCI Firmware, r3.3, sec 4.1.2).  This
> means PCI extended config space (offsets 0x100-0xfff) may not be accessible.
> 
> Some firmware doesn't report ECAM space via PNP0C02 _CRS methods, but does
> mention it as an EfiMemoryMappedIO region via EFI GetMemoryMap(), which is
> normally converted to an E820 entry by a bootloader or EFI stub.
> 
> 07eab0901ede ("efi/x86: Remove EfiMemoryMappedIO from E820 map"), removes
> E820 entries that correspond to EfiMemoryMappedIO regions because some
> other firmware uses EfiMemoryMappedIO for PCI host bridge windows, and the
> E820 entries prevent Linux from allocating BAR space for hot-added devices.
> 
> Allow use of ECAM for extended config space when the region is covered by
> an EfiMemoryMappedIO region, even if it's not included in E820 or PNP0C02
> _CRS.
> 
> Reported by Kan Liang, Tony Luck, and Giovanni Cabiddu.
> 
> Fixes: 07eab0901ede ("efi/x86: Remove EfiMemoryMappedIO from E820 map")
> Link: https://lore.kernel.org/r/ac2693d8-8ba3-72e0-5b66-b3ae008d539d@linux.intel.com
> Reported-by: Kan Liang <kan.liang@linux.intel.com>
> Reported-by: Tony Luck <tony.luck@intel.com>
> Reported-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>

> ---
>  arch/x86/pci/mmconfig-shared.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/arch/x86/pci/mmconfig-shared.c b/arch/x86/pci/mmconfig-shared.c
> index cd16bef5f2d9..da4b6e8e9df0 100644
> --- a/arch/x86/pci/mmconfig-shared.c
> +++ b/arch/x86/pci/mmconfig-shared.c
> @@ -12,6 +12,7 @@
>   */
>  
>  #include <linux/acpi.h>
> +#include <linux/efi.h>
>  #include <linux/pci.h>
>  #include <linux/init.h>
>  #include <linux/bitmap.h>
> @@ -442,6 +443,32 @@ static bool is_acpi_reserved(u64 start, u64 end, enum e820_type not_used)
>  	return mcfg_res.flags;
>  }
>  
> +static bool is_efi_mmio(u64 start, u64 end, enum e820_type not_used)
> +{
> +#ifdef CONFIG_EFI
> +	efi_memory_desc_t *md;
> +	u64 size, mmio_start, mmio_end;
> +
> +	for_each_efi_memory_desc(md) {
> +		if (md->type == EFI_MEMORY_MAPPED_IO) {
> +			size = md->num_pages << EFI_PAGE_SHIFT;
> +			mmio_start = md->phys_addr;
> +			mmio_end = mmio_start + size;
> +
> +			/*
> +			 * N.B. Caller supplies (start, start + size),
> +			 * so to match, mmio_end is the first address
> +			 * *past* the EFI_MEMORY_MAPPED_IO area.
> +			 */
> +			if (mmio_start <= start && end <= mmio_end)
> +				return true;
> +		}
> +	}
> +#endif
> +
> +	return false;
> +}
> +
>  typedef bool (*check_reserved_t)(u64 start, u64 end, enum e820_type type);
>  
>  static bool __ref is_mmconf_reserved(check_reserved_t is_reserved,
> @@ -513,6 +540,10 @@ pci_mmcfg_check_reserved(struct device *dev, struct pci_mmcfg_region *cfg, int e
>  			       "MMCONFIG at %pR not reserved in "
>  			       "ACPI motherboard resources\n",
>  			       &cfg->res);
> +
> +		if (is_mmconf_reserved(is_efi_mmio, cfg, dev,
> +				       "EfiMemoryMappedIO"))
> +			return true;
>  	}
>  
>  	/*
>