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

[Tom Lendacky <thomas.lendacky@amd.com>]

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@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...

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

Thanks,
Tom

>