This patch adds a Documenation entry to decribe the AMD Secure Memory Encryption (SME) feature. Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx> --- Documentation/x86/amd-memory-encryption.txt | 35 +++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) create mode 100644 Documentation/x86/amd-memory-encryption.txt diff --git a/Documentation/x86/amd-memory-encryption.txt b/Documentation/x86/amd-memory-encryption.txt new file mode 100644 index 0000000..f19c555 --- /dev/null +++ b/Documentation/x86/amd-memory-encryption.txt @@ -0,0 +1,35 @@ +Secure Memory Encryption (SME) is a feature found on AMD processors. + +SME provides the ability to mark individual pages of memory as encrypted using +the standard x86 page tables. A page that is marked encrpyted will be +automatically decrypted when read from DRAM and encrypted when written to +DRAM. SME can therefore be used to protect the contents of DRAM from physical +attacks on the system. + +Support for SME can be determined through the CPUID instruction. The CPUID +function 0x8000001f reports information related to SME: + + 0x8000001f[eax]: + Bit[0] indicates support for SME + 0x8000001f[ebx]: + Bit[5:0] pagetable bit number used to enable memory encryption + Bit[11:6] reduction in physical address space, in bits, when + memory encryption is enabled (this only affects system + physical addresses, not guest physical addresses) + +If support for SME is present, MSR 0xc00100010 (SYS_CFG) can be used to +determine if SME is enabled and/or to enable memory encryption: + + 0xc0010010: + Bit[23] 0 = memory encryption features are disabled + 1 = memory encryption features are enabled + +Linux relies on BIOS to set this bit if BIOS has determined that the reduction +in the physical address space as a result of enabling memory encryption (see +CPUID information above) will not conflict with the address space resource +requirements for the system. If this bit is not set upon Linux startup then +Linux itself will not set it and memory encryption will not be possible. + +SME support is configurable in the kernel through the AMD_MEM_ENCRYPT config +option. Additionally, the mem_encrypt=on command line parameter is required +to activate memory encryption. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
