Messages in this thread | | | Subject | Re: [RFC PATCH v4 15/28] Add support to access persistent memory in the clear | From | Tom Lendacky <> | Date | Thu, 23 Mar 2017 16:02:53 -0500 |
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On 3/17/2017 5:58 PM, Elliott, Robert (Persistent Memory) wrote: > > >> -----Original Message----- >> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel- >> owner@vger.kernel.org] On Behalf Of Tom Lendacky >> Sent: Thursday, February 16, 2017 9:45 AM >> Subject: [RFC PATCH v4 15/28] Add support to access persistent memory in >> the clear >> >> Persistent memory is expected to persist across reboots. The encryption >> key used by SME will change across reboots which will result in corrupted >> persistent memory. Persistent memory is handed out by block devices >> through memory remapping functions, so be sure not to map this memory as >> encrypted. > > The system might be able to save and restore the correct encryption key for a > region of persistent memory, in which case it does need to be mapped as > encrypted.
If the OS could get some indication that BIOS/UEFI has saved and restored the encryption key, then it could be mapped encrypted.
> > This might deserve a new EFI_MEMORY_ENCRYPTED attribute bit so the > system firmware can communicate that information to the OS (in the > UEFI memory map and the ACPI NFIT SPA Range structures). It wouldn't > likely ever be added to the E820h table - ACPI 6.1 already obsoleted the > Extended Attribute for AddressRangeNonVolatile.
An attribute bit in some form would be a nice way to inform the OS that the persistent memory can be mapped encrypted.
> >> >> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> >> --- >> arch/x86/mm/ioremap.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c >> index b0ff6bc..c6cb921 100644 >> --- a/arch/x86/mm/ioremap.c >> +++ b/arch/x86/mm/ioremap.c >> @@ -498,6 +498,8 @@ static bool >> memremap_should_map_encrypted(resource_size_t phys_addr, >> case E820_TYPE_ACPI: >> case E820_TYPE_NVS: >> case E820_TYPE_UNUSABLE: >> + case E820_TYPE_PMEM: >> + case E820_TYPE_PRAM: >> return false; >> default: >> break; > > E820_TYPE_RESERVED is also used to report persistent memory in > some systems (patch 16 adds that for other reasons). > > You might want to intercept the persistent memory types in the > efi_mem_type(phys_addr) switch statement earlier in the function > as well. https://lkml.org/lkml/2017/3/13/357 recently mentioned that > "in qemu hotpluggable memory isn't put into E820," with the latest > information only in the UEFI memory map. > > Persistent memory can be reported there as: > * EfiReservedMemoryType type with the EFI_MEMORY_NV attribute > * EfiPersistentMemory type with the EFI_MEMORY_NV attribute > > Even the UEFI memory map is not authoritative, though. To really > determine what is in these regions requires parsing the ACPI NFIT > SPA Ranges structures. Parts of the E820 or UEFI regions could be > reported as volatile there and should thus be encrypted.
Thanks for the details on this. I'll take a closer look at this and update the checks appropriately.
Thanks, Tom
> > --- > Robert Elliott, HPE Persistent Memory > > >
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