[PATCH 1/2] firmware/efi: Tell memblock about EFI reservations

[Moritz Fischer]

Marc,

On Thu, Apr 29, 2021 at 02:35:32PM +0100, Marc Zyngier wrote:
> kexec_load_file() relies on the memblock infrastructure to avoid
> stamping over regions of memory that are essential to the survival
> of the system.
> 
> However, nobody seems to agree how to flag these regions as reserved,
> and (for example) EFI only publishes its reservations in /proc/iomem
> for the benefit of the traditional, userspace based kexec tool.
> 
> On arm64 platforms with GICv3, this can result in the payload being
> placed at the location of the LPI tables. Shock, horror!
> 
> Let's augment the EFI reservation code with a memblock_reserve() call,
> protecting our dear tables from the secondary kernel invasion.
> 
> At some point, someone will have to go and figure out a way to unify
> these multiple reservation trees, because sprinkling random reservation
> calls is only a temporary workaround.
> 

Feel free to add (and/or):

Reported-by: Moritz Fischer <mdf at kernel.org>
Tested-by: Moritz Fischer <mdf at kernel.org>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  drivers/firmware/efi/efi.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 4b7ee3fa9224..026b02f5f7d8 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -896,11 +896,25 @@ static int __init efi_memreserve_map_root(void)
>  static int efi_mem_reserve_iomem(phys_addr_t addr, u64 size)
>  {
>  	struct resource *res, *parent;
> +	int ret;
>  
>  	res = kzalloc(sizeof(struct resource), GFP_ATOMIC);
>  	if (!res)
>  		return -ENOMEM;
>  
> +	/*
> +	 * Given that efi_mem_reserve_iomem() can be called at any
> +	 * time, only call memblock_reserve() if the architecture
> +	 * keeps the infrastructure around.
> +	 */
> +	if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
> +		ret = memblock_reserve(addr, size);
> +		if (ret) {
> +			kfree(res);
> +			return ret;
> +		}
> +	}
> +
>  	res->name	= "reserved";
>  	res->flags	= IORESOURCE_MEM;
>  	res->start	= addr;
> @@ -908,7 +922,14 @@ static int efi_mem_reserve_iomem(phys_addr_t addr, u64 size)
>  
>  	/* we expect a conflict with a 'System RAM' region */
>  	parent = request_resource_conflict(&iomem_resource, res);
> -	return parent ? request_resource(parent, res) : 0;
> +	ret = parent ? request_resource(parent, res) : 0;
> +	if (ret) {
> +		kfree(res);
> +		if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK))
> +			memblock_free(addr, size);
> +	}
> +
> +	return ret;
>  }
>  
>  int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
> -- 
> 2.29.2
> 
> 
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Thanks,
Moritz