[RFC,v2,0/7] Support nested SNP KVM guests on Hyper-V

This patch series enables SNP-host support when running on Hyper-V, which
allows launching SNP guests while running as a nested hypervisor. This works
with SNP guest side support that was merged in v5.19, and the snp capable qemu
from AMD.

In this scenario the L0 hypervisor is Hyper-V, L1 is KVM, and L2 is an SNP
guest. The code from this patchset runs in L1. L1 is not an SNP guest itself,
SNP guests are not capable of supporting virtualization.

Patch 1 deals with allocating an RMP table which is not provided by
firmware/hypervisor, but is needed by the kernel to keep track of page
assignment to guests and rmp page size. Patch 2 implements MSR-based
rmpupdate/psmash instructions which are meant for virtualized environments.
Patch 3 containts the logic to update the rmp table when rmpupdate/psmash is
issued. Patch 4 makes sure that the kernel does not disable SNP support during
early CPU init. Patch 5 allows SNP initialization to proceed when no iommus
are available. Patch 6 adds a quirk in psp command buffer handling, because of
differences in SNP firmware spec interpretation. Patch 7 adds handling for RMP
faults which occur as NPF and the L0 is not able to resolve the address that
the fault occurred at.

This series depends on:

- "Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support" (applies on top of RFC v7)
  https://lore.kernel.org/lkml/20221214194056.161492-1-michael.roth@amd.com/
- "Support ACPI PSP on Hyper-V"
  https://lore.kernel.org/lkml/20230213092429.1167812-1-jpiotrowski@linux.microsoft.com/

Changes since v1:
* added handling for rmp page faults that occur during copy_to_user() that
  don't come with a proper fault address when running nested.
* fold IS_ENABLED() test into hv_needs_snp_rmp(), and use CONFIG_KVM_AMD_SEV
  instead of CONFIG_AMD_MEM_ENCRYPT
* introduce snp_soft_rmptable() wrapper to remove core dependency on hyperv
  specific code
* use msr_set_bit for SYSCFG_MEM_ENCRYPT bit instead of open coding

Jeremi Piotrowski (7):
  x86/hyperv: Allocate RMP table during boot
  x86/sev: Add support for NestedVirtSnpMsr
  x86/sev: Maintain shadow rmptable on Hyper-V
  x86/amd: Configure necessary MSRs for SNP during CPU init when running
    as a guest
  iommu/amd: Don't fail snp_enable when running virtualized
  crypto: ccp - Introduce quirk to always reclaim pages after SEV-legacy
    commands
  x86/fault: Handle RMP faults with 0 address when nested

 arch/x86/hyperv/hv_init.c          |   5 +
 arch/x86/include/asm/cpufeatures.h |   1 +
 arch/x86/include/asm/hyperv-tlfs.h |   3 +
 arch/x86/include/asm/mshyperv.h    |   3 +
 arch/x86/include/asm/msr-index.h   |   2 +
 arch/x86/include/asm/sev.h         |   6 ++
 arch/x86/kernel/cpu/amd.c          |   5 +-
 arch/x86/kernel/cpu/mshyperv.c     |  47 +++++++++
 arch/x86/kernel/sev.c              | 150 ++++++++++++++++++++++++++---
 arch/x86/mm/fault.c                |  14 +++
 drivers/crypto/ccp/sev-dev.c       |   6 +-
 drivers/crypto/ccp/sp-dev.h        |   4 +
 drivers/crypto/ccp/sp-platform.c   |   1 +
 drivers/iommu/amd/init.c           |   6 ++
 14 files changed, 240 insertions(+), 13 deletions(-)