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    SubjectRe: [RFC PATCH v2 01/20] x86: Documentation for AMD Secure Memory Encryption (SME)
    On Mon, Aug 22, 2016 at 05:35:39PM -0500, Tom Lendacky wrote:
    > 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

    s/encrpyted/encrypted/

    > +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.

    " ... is configurable through CONFIG_AMD_MEM_ENCRYPT."

    > Additionally, the mem_encrypt=on command line parameter is required
    > +to activate memory encryption.

    I think you want to rewrite the logic here to say that people should use
    the BIOS option and if none is present for whatever reason, resort to
    the alternative "mem_encrypt=on" kernel command line option, no?

    --
    Regards/Gruss,
    Boris.

    ECO tip #101: Trim your mails when you reply.
    --

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