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

[Tom Lendacky]

On 8/1/2017 11:02 PM, Borislav Petkov wrote:
> On Mon, Jul 24, 2017 at 02:07:51PM -0500, Brijesh Singh wrote:
> > From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> >
> > 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@xxxxxxx>
> > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > ---
> >   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...

Let me look into this.  I can probably come up with something that does
the walk once.

Thanks,
Tom

>