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    Subject[RFC PATCH v2 01/20] x86: Documentation for AMD Secure Memory Encryption (SME)
    Date
    This patch adds a Documenation entry to decribe the AMD Secure Memory
    Encryption (SME) feature.

    Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
    ---
    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.
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