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

Borislav Petkov
2017-08-02T04:02:56Z

On Mon, Jul 24, 2017 at 02:07:51PM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
>
> 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-5C7GfCeVMHo@public.gmane.org>
> Signed-off-by: Brijesh Singh <brijesh.singh-5C7GfCeVMHo@public.gmane.org>
> ---
> 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)
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