Re: [RFC Part1 PATCH v3 11/17] x86/mm, resource: Use PAGE_KERNEL protection for ioremap of memory pages

[Borislav Petkov <bp@suse.de>]

On Mon, Jul 24, 2017 at 02:07:51PM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> In order for memory pages to be properly mapped when SEV is active, we
> need to use the PAGE_KERNEL protection attribute as the base protection.
> This will insure that memory mapping of, e.g. ACPI tables, receives the
> proper mapping attributes.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  arch/x86/mm/ioremap.c  | 28 ++++++++++++++++++++++++++++
>  include/linux/ioport.h |  3 +++
>  kernel/resource.c      | 17 +++++++++++++++++
>  3 files changed, 48 insertions(+)
> 
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index c0be7cf..7b27332 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -69,6 +69,26 @@ static int __ioremap_check_ram(unsigned long start_pfn, unsigned long nr_pages,
>  	return 0;
>  }
>  
> +static int __ioremap_res_desc_other(struct resource *res, void *arg)
> +{
> +	return (res->desc != IORES_DESC_NONE);
> +}
> +
> +/*
> + * This function returns true if the target memory is marked as
> + * IORESOURCE_MEM and IORESOURCE_BUSY and described as other than
> + * IORES_DESC_NONE (e.g. IORES_DESC_ACPI_TABLES).
> + */
> +static bool __ioremap_check_if_mem(resource_size_t addr, unsigned long size)
> +{
> +	u64 start, end;
> +
> +	start = (u64)addr;
> +	end = start + size - 1;
> +
> +	return (walk_mem_res(start, end, NULL, __ioremap_res_desc_other) == 1);
> +}
> +
>  /*
>   * Remap an arbitrary physical address space into the kernel virtual
>   * address space. It transparently creates kernel huge I/O mapping when
> @@ -146,7 +166,15 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
>  		pcm = new_pcm;
>  	}
>  
> +	/*
> +	 * If the page being mapped is in memory and SEV is active then
> +	 * make sure the memory encryption attribute is enabled in the
> +	 * resulting mapping.
> +	 */
>  	prot = PAGE_KERNEL_IO;
> +	if (sev_active() && __ioremap_check_if_mem(phys_addr, size))
> +		prot = pgprot_encrypted(prot);

Hmm, so this function already does walk_system_ram_range() a bit
earlier and now on SEV systems we're going to do it again. Can we make
walk_system_ram_range() return a distinct value for SEV systems and act
accordingly in __ioremap_caller() instead of repeating the operation?

It looks to me like we could...

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--