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

From: Jeremi Piotrowski
Date: Mon Feb 13 2023 - 05:34:29 EST


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@xxxxxxx/
- "Support ACPI PSP on Hyper-V"
https://lore.kernel.org/lkml/20230213092429.1167812-1-jpiotrowski@xxxxxxxxxxxxxxxxxxx/

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(-)

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2.25.1