On 11/10/2016 4:51 AM, Borislav Petkov wrote: > On Wed, Nov 09, 2016 at 06:34:39PM -0600, 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@xxxxxxx> >> --- >> Documentation/kernel-parameters.txt | 5 +++ >> Documentation/x86/amd-memory-encryption.txt | 40 +++++++++++++++++++++++++++ >> 2 files changed, 45 insertions(+) >> create mode 100644 Documentation/x86/amd-memory-encryption.txt >> >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt >> index 030e9e9..4c730b0 100644 >> --- a/Documentation/kernel-parameters.txt >> +++ b/Documentation/kernel-parameters.txt >> @@ -2282,6 +2282,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. >> memory contents and reserves bad memory >> regions that are detected. >> >> + mem_encrypt= [X86-64] Enable AMD Secure Memory Encryption (SME) >> + Memory encryption is disabled by default, using this >> + switch, memory encryption can be enabled. > > I'd say here: > > "Force-enable memory encryption if it is disabled in the > BIOS." Good suggestion, that will make this clearer. > >> + on: enable memory encryption >> + >> meye.*= [HW] Set MotionEye Camera parameters >> See Documentation/video4linux/meye.txt. >> >> diff --git a/Documentation/x86/amd-memory-encryption.txt b/Documentation/x86/amd-memory-encryption.txt >> new file mode 100644 >> index 0000000..788d871 >> --- /dev/null >> +++ b/Documentation/x86/amd-memory-encryption.txt >> @@ -0,0 +1,40 @@ >> +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 encrypted 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. >> + >> +A page is encrypted when a page table entry has the encryption bit set (see >> +below how to determine the position of the bit). The encryption bit can be >> +specified in the cr3 register, allowing the PGD table to be encrypted. Each >> +successive level of page tables can also be encrypted. >> + >> +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 through the AMD_MEM_ENCRYPT config option. >> +Additionally, the mem_encrypt=on command line parameter is required to activate >> +memory encryption. > > So how am I to understand this? We won't have TSME or we will but it > will be off by default and users will have to enable it in the BIOS or > will have to boot with mem_encrypt=on...? > > Can you please expand on all the possible options there would be > available to users? Yup, I'll try to expand on the documentation to include all the possibilities for this. Thanks, Tom > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
