Merge tag 'x86_urgent_for_v6.2_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Borislav Petkov:

 - Start checking for -mindirect-branch-cs-prefix clang support too now
   that LLVM 16 will support it

 - Fix a NULL ptr deref when suspending with Xen PV

 - Have a SEV-SNP guest check explicitly for features enabled by the
   hypervisor and fail gracefully if some are unsupported by the guest
   instead of failing in a non-obvious and hard-to-debug way

 - Fix a MSI descriptor leakage under Xen

 - Mark Xen's MSI domain as supporting MSI-X

 - Prevent legacy PIC interrupts from being resent in software by
   marking them level triggered, as they should be, which lead to a NULL
   ptr deref

* tag 'x86_urgent_for_v6.2_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/build: Move '-mindirect-branch-cs-prefix' out of GCC-only block
  acpi: Fix suspend with Xen PV
  x86/sev: Add SEV-SNP guest feature negotiation support
  x86/pci/xen: Fixup fallout from the PCI/MSI overhaul
  x86/pci/xen: Set MSI_FLAG_PCI_MSIX support in Xen MSI domain
  x86/i8259: Mark legacy PIC interrupts with IRQ_LEVEL

1 files changed, 36 insertions, 0 deletions

diff --git a/Documentation/x86/amd-memory-encryption.rst b/Documentation/x86/amd-memory-encryption.rst
index a1940ebe7be5..934310ce7258 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.
+
++-----------------+---------------+---------------+------------------+
+| 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.pdf