Re: [RFC PATCH v1 04/21] RISC-V: ACPI: Enhance acpi_os_ioremap with MMIO remapping

[Andrew Jones]

On Thu, Aug 03, 2023 at 11:28:59PM +0530, Sunil V L wrote:
> Enhance the acpi_os_ioremap() to support opregions in MMIO
> space. Also, have strict checks using EFI memory map
> to allow remapping the RAM similar to arm64.
> 
> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Cc: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> 
> Signed-off-by: Sunil V L <sunilvl@xxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/Kconfig       |  1 +
>  arch/riscv/kernel/acpi.c | 86 +++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 86 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 318f62a0a187..e19f32c12a68 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -38,6 +38,7 @@ config RISCV
>  	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
>  	select ARCH_HAS_VDSO_DATA
> +	select ARCH_KEEP_MEMBLOCK
>  	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
>  	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
>  	select ARCH_STACKWALK
> diff --git a/arch/riscv/kernel/acpi.c b/arch/riscv/kernel/acpi.c
> index 56cb2c986c48..aa4433bca6d9 100644
> --- a/arch/riscv/kernel/acpi.c
> +++ b/arch/riscv/kernel/acpi.c
> @@ -17,6 +17,7 @@
>  #include <linux/io.h>
>  #include <linux/pci.h>
>  #include <linux/efi.h>
> +#include <linux/memblock.h>
>  
>  int acpi_noirq = 1;		/* skip ACPI IRQ initialization */
>  int acpi_disabled = 1;
> @@ -217,7 +218,90 @@ void __init __acpi_unmap_table(void __iomem *map, unsigned long size)
>  
>  void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
>  {
> -	return (void __iomem *)memremap(phys, size, MEMREMAP_WB);
> +	efi_memory_desc_t *md, *region = NULL;
> +	pgprot_t prot;
> +
> +	if (WARN_ON_ONCE(!efi_enabled(EFI_MEMMAP)))
> +		return NULL;
> +
> +	for_each_efi_memory_desc(md) {
> +		u64 end = md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT);
> +
> +		if (phys < md->phys_addr || phys >= end)
> +			continue;
> +
> +		if (phys + size > end) {
> +			pr_warn(FW_BUG "requested region covers multiple EFI memory regions\n");
> +			return NULL;
> +		}
> +		region = md;
> +		break;
> +	}
> +
> +	/*
> +	 * It is fine for AML to remap regions that are not represented in the
> +	 * EFI memory map at all, as it only describes normal memory, and MMIO
> +	 * regions that require a virtual mapping to make them accessible to
> +	 * the EFI runtime services.
> +	 */
> +	prot = PAGE_KERNEL_IO;
> +	if (region) {
> +		switch (region->type) {
> +		case EFI_LOADER_CODE:
> +		case EFI_LOADER_DATA:
> +		case EFI_BOOT_SERVICES_CODE:
> +		case EFI_BOOT_SERVICES_DATA:
> +		case EFI_CONVENTIONAL_MEMORY:
> +		case EFI_PERSISTENT_MEMORY:
> +			if (memblock_is_map_memory(phys) ||
> +			    !memblock_is_region_memory(phys, size)) {
> +				pr_warn(FW_BUG "requested region covers kernel memory @ %p\n",
> +					&phys);
> +				return NULL;
> +			}
> +
> +			/*
> +			 * Mapping kernel memory is permitted if the region in
> +			 * question is covered by a single memblock with the
> +			 * NOMAP attribute set: this enables the use of ACPI
> +			 * table overrides passed via initramfs.
> +			 * This particular use case only requires read access.
> +			 */
> +			fallthrough;
> +
> +		case EFI_RUNTIME_SERVICES_CODE:
> +			/*
> +			 * This would be unusual, but not problematic per se,
> +			 * as long as we take care not to create a writable
> +			 * mapping for executable code.
> +			 */
> +			prot = PAGE_KERNEL_RO;
> +			break;
> +
> +		case EFI_ACPI_RECLAIM_MEMORY:
> +			/*
> +			 * ACPI reclaim memory is used to pass firmware tables
> +			 * and other data that is intended for consumption by
> +			 * the OS only, which may decide it wants to reclaim
> +			 * that memory and use it for something else. We never
> +			 * do that, but we usually add it to the linear map
> +			 * anyway, in which case we should use the existing
> +			 * mapping.
> +			 */
> +			if (memblock_is_map_memory(phys))
> +				return (void __iomem *)__va(phys);
> +			fallthrough;
> +
> +		default:
> +			if (region->attribute & EFI_MEMORY_WB)
> +				prot = PAGE_KERNEL;
> +			else if ((region->attribute & EFI_MEMORY_WC) ||
> +				 (region->attribute & EFI_MEMORY_WT))
> +				prot = pgprot_writecombine(PAGE_KERNEL);
> +		}
> +	}
> +
> +	return ioremap_prot(phys, size, pgprot_val(prot));
>  }
>  
>  #ifdef CONFIG_PCI
> -- 
> 2.39.2
>

Such a faithful port of arm64's function that it begs the question as to
whether or not we should refactor and share. Anyway, other than Andy's
comments, LGTM

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>

Thanks,
drew