Re: [PATCH v7 2/7] x86/sgx: Add infrastructure to identify SGX EPC pages

[Jarkko Sakkinen <jarkko@kernel.org>]

On Mon, 2021-09-27 at 14:34 -0700, Tony Luck wrote:
> X86 machine check architecture reports a physical address when there
> is a memory error. Handling that error requires a method to determine
> whether the physical address reported is in any of the areas reserved
> for EPC pages by BIOS.
> 
> SGX EPC pages do not have Linux "struct page" associated with them.
> 
> Keep track of the mapping from ranges of EPC pages to the sections
> that contain them using an xarray.
> 
> Create a function arch_is_platform_page() that simply reports whether an address
> is an EPC page for use elsewhere in the kernel. The ACPI error injection
> code needs this function and is typically built as a module, so export it.
> 
> Note that arch_is_platform_page() will be slower than other similar "what type
> is this page" functions that can simply check bits in the "struct page".
> If there is some future performance critical user of this function it
> may need to be implemented in a more efficient way.
> 
> Note also that the current implementation of xarray allocates a few
> hundred kilobytes for this usage on a system with 4GB of SGX EPC memory
> configured. This isn't ideal, but worth it for the code simplicity.
> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index d18988a46c13..09fa42690ff2 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -20,6 +20,7 @@ struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
>  static int sgx_nr_epc_sections;
>  static struct task_struct *ksgxd_tsk;
>  static DECLARE_WAIT_QUEUE_HEAD(ksgxd_waitq);
> +static DEFINE_XARRAY(sgx_epc_address_space);
>  
>  /*
>   * These variables are part of the state of the reclaimer, and must be accessed
> @@ -650,6 +651,8 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
>  	}
>  
>  	section->phys_addr = phys_addr;
> +	xa_store_range(&sgx_epc_address_space, section->phys_addr,
> +		       phys_addr + size - 1, section, GFP_KERNEL);
>  
>  	for (i = 0; i < nr_pages; i++) {
>  		section->pages[i].section = index;
> @@ -661,6 +664,12 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
>  	return true;
>  }
>  
> +bool arch_is_platform_page(u64 paddr)
> +{
> +	return !!xa_load(&sgx_epc_address_space, paddr);
> +}
> +EXPORT_SYMBOL_GPL(arch_is_platform_page);
> +
>  /**
>   * A section metric is concatenated in a way that @low bits 12-31 define the
>   * bits 12-31 of the metric and @high bits 0-19 define the bits 32-51 of the

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

/Jarkko