On Mon, 16 Jan 2023 13:53:56 +0530 "Nikunj A. Dadhania" <nikunj@xxxxxxx> wrote: > On 13/01/23 17:23, Zhi Wang wrote: > > On Thu, 12 Jan 2023 14:11:39 +0530 > > Nikunj A Dadhania <nikunj@xxxxxxx> wrote: > > > > >> diff --git a/Documentation/x86/amd-memory-encryption.rst > >> b/Documentation/x86/amd-memory-encryption.rst index > >> a1940ebe7be5..b3adc39d7735 100644 --- > >> a/Documentation/x86/amd-memory-encryption.rst +++ > >> b/Documentation/x86/amd-memory-encryption.rst @@ -95,3 +95,39 @@ by > >> supplying mem_encrypt=on on the kernel command line. However, if BIOS > >> does not enable SME, then Linux will not be able to activate memory > >> encryption, even if configured to do so by default or the mem_encrypt=on > >> command line parameter is specified. + > >> +Secure Nested Paging (SNP) > >> +========================== > >> + > >> +SEV-SNP introduces new features (SEV_FEATURES[1:63]) which can be > >> enabled +by the hypervisor for security enhancements. Some of these > >> features need +guest side implementation to function correctly. The > >> below table lists the +expected guest behavior with various possible > >> scenarios of guest/hypervisor +SNP feature support. > >> + > > > "guest needs implementation" seems a little bit confusing. I suppose it > > means the feature is mandatory for the guest. > > That is not correct. None of these features are mandatory for the guest. > The hypervisor can enable this feature without the knowledge of guest > kernel support. So there should be a mechanism in the guest to detect this > and fail the boot if needed. > > > If so, on the second row > > guest can boot without it. Some explanation? > > In the first and second row, HV has not enabled the feature, so the > guest should boot fine irrespective of "Guest needs implementation". > Feel free to educate me if I understand correctly or not: There are two kinds of features in SEV_FEATURES: 1. Features that HV can freely enable/disable and they won't distrub the guest. HV | Guest needs impl | Guest has impl | Result Y/N N X (not necessary) Boot 2. Features that a guest has to be aware of and handle when HV enables them. HV | Guest needs impl | Guest has impl | Result N Y X (Dont care) Boot Y Y N Fail Y Y Y Boot > >> +| No | No | No | Boot | > > >> +| No | Yes | No | Boot | > > > >> ++-----------------+---------------+---------------+------------------+ > >> +| Feature Enabled | Guest needs | Guest has | Guest boot | > >> +| by the HV | implementation| implementation| behaviour | > >> ++=================+===============+===============+==================+>> +| No | No | No | Boot | > >> +| | | | | > >> ++-----------------+---------------+---------------+------------------+ > >> +| No | Yes | No | Boot | > >> +| | | | | > >> ++-----------------+---------------+---------------+------------------+ > >> +| No | Yes | Yes | Boot | > >> +| | | | | > >> ++-----------------+---------------+---------------+------------------+ > >> +| Yes | No | No | Boot with | > >> +| | | | feature enabled | > >> ++-----------------+---------------+---------------+------------------+ > >> +| Yes | Yes | No | Graceful boot | > >> +| | | | failure | > >> ++-----------------+---------------+---------------+------------------+ > >> +| Yes | Yes | Yes | Boot with | > >> +| | | | feature enabled | > >> ++-----------------+---------------+---------------+------------------+ > >> + > >> +More details in AMD64 APM[1] Vol 2: 15.34.10 SEV_STATUS MSR > >> + > >> +[1] https://www.amd.com/system/files/TechDocs/40332_4.05.pdf > > > > Probably update the link here as well. > > Sure. > > >> diff --git a/arch/x86/include/uapi/asm/svm.h > >> b/arch/x86/include/uapi/asm/svm.h index f69c168391aa..a04fe07eb9a8 100644 > >> --- a/arch/x86/include/uapi/asm/svm.h > >> +++ b/arch/x86/include/uapi/asm/svm.h > >> @@ -116,6 +116,12 @@ > >> #define SVM_VMGEXIT_AP_CREATE 1 > >> #define SVM_VMGEXIT_AP_DESTROY 2 > >> #define SVM_VMGEXIT_HV_FEATURES 0x8000fffd > >> +#define SVM_VMGEXIT_TERM_REQUEST 0x8000fffe > >> +#define SVM_VMGEXIT_TERM_REASON(reason_set, reason_code) \ > >> + /* SW_EXITINFO1[3:0] */ \ > >> + (((((u64)reason_set) & 0xf)) | \ > > ^ > > One extra space before 0xf should be removed. > > Sure. > > Thanks for the review. > > Nikunj >
