On 02/16/2017 11:56 AM, Borislav Petkov wrote: > Ok, this time detailed review :-) > > On Thu, Feb 16, 2017 at 09:42:11AM -0600, Tom Lendacky wrote: >> This patch adds a Documenation entry to decribe the AMD Secure Memory >> Encryption (SME) feature. > > Please introduce a spellchecker into your patch creation workflow. I see > two typos in one line. > > Also, never start patch commit messages with "This patch" - we know it > is this patch. Always write a doer-sentences explaining the why, not the > what. Something like: > > "Add a SME and mem_encrypt= kernel parameter documentation." > > for example. Ok, will do. > >> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx> >> --- >> Documentation/admin-guide/kernel-parameters.txt | 11 ++++ >> Documentation/x86/amd-memory-encryption.txt | 57 +++++++++++++++++++++++ >> 2 files changed, 68 insertions(+) >> create mode 100644 Documentation/x86/amd-memory-encryption.txt >> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt >> index 110745e..91c40fa 100644 >> --- a/Documentation/admin-guide/kernel-parameters.txt >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -2145,6 +2145,17 @@ >> memory contents and reserves bad memory >> regions that are detected. >> >> + mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control >> + Valid arguments: on, off >> + Default (depends on kernel configuration option): >> + on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) >> + off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) >> + mem_encrypt=on: Activate SME >> + mem_encrypt=off: Do not activate SME >> + >> + Refer to the SME documentation for details on when > > "Refer to Documentation/x86/amd-memory-encryption.txt .." Ok. > >> + memory encryption can be activated. >> + >> mem_sleep_default= [SUSPEND] Default system suspend mode: >> s2idle - Suspend-To-Idle >> shallow - Power-On Suspend or equivalent (if supported) >> diff --git a/Documentation/x86/amd-memory-encryption.txt b/Documentation/x86/amd-memory-encryption.txt >> new file mode 100644 >> index 0000000..0938e89 >> --- /dev/null >> +++ b/Documentation/x86/amd-memory-encryption.txt >> @@ -0,0 +1,57 @@ >> +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 > > "... how to determine its position)." Ok. > >> +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 activate memory >> + encryption > > s/Bit/Bits/ Ok. > >> + Bit[11:6] reduction in physical address space, in bits, when > > Ditto. > >> + 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 > > Let's use the kernel's define name MSR_K8_SYSCFG to avoid ambiguity. Will do. > >> +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. >> + >> +The state of SME in the Linux kernel can be documented as follows: >> + - Supported: >> + The CPU supports SME (determined through CPUID instruction). >> + >> + - Enabled: >> + Supported and bit 23 of the SYS_CFG MSR is set. > > Ditto. > >> + >> + - Active: >> + Supported, Enabled and the Linux kernel is actively applying >> + the encryption bit to page table entries (the SME mask in the >> + kernel is non-zero). >> + >> +SME can also be enabled and activated in the BIOS. If SME is enabled and >> +activated in the BIOS, then all memory accesses will be encrypted and it will >> +not be necessary to activate the Linux memory encryption support. If the BIOS >> +merely enables SME (sets bit 23 of the SYS_CFG MSR), then Linux can activate >> +memory encryption. > > "... This is done by supplying mem_encrypt=on on the kernel command line. > Alternatively, if the kernel should enable SME by default, set > CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y." Yup, much clearer. > >> However, if BIOS does not enable SME, then Linux will not >> +attempt to activate memory encryption, even if configured to do so by default > > will not attempt or will not be able to? Probably closer to will not be able to right now. I'll update that. Thanks, Tom > >> +or the mem_encrypt=on command line parameter is specified. >
