Re: [PATCH RFC v9 07/51] x86/sev: Add the host SEV-SNP initialization support

Borislav Petkov
2023-06-21T09:43:36Z

On Sun, Jun 11, 2023 at 11:25:15PM -0500, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@amd.com>
>
> The memory integrity guarantees of SEV-SNP are enforced through a new
> structure called the Reverse Map Table (RMP). The RMP is a single data
> structure shared across the system that contains one entry for every 4K
> page of DRAM that may be used by SEV-SNP VMs. APM2 section 15.36 details

Rather say 'APM v2, section "Secure Nested Paging (SEV-SNP)"' because
the numbering is more likely to change than the name in the future. With
the name, people can find it faster.

> a number of steps needed to detect/enable SEV-SNP and RMP table support
> on the host:
>
> - Detect SEV-SNP support based on CPUID bit
> - Initialize the RMP table memory reported by the RMP base/end MSR
> registers and configure IOMMU to be compatible with RMP access
> restrictions
> - Set the MtrrFixDramModEn bit in SYSCFG MSR
> - Set the SecureNestedPagingEn and VMPLEn bits in the SYSCFG MSR
> - Configure IOMMU
>
> RMP table entry format is non-architectural and it can vary by
> processor. It is defined by the PPR. Restrict SNP support to CPU
> models/families which are compatible with the current RMP table entry
> format to guard against any undefined behavior when running on other
> system types. Future models/support will handle this through an
> architectural mechanism to allow for broader compatibility.

I'm guessing this is all for live migration between SNP hosts. If so,
then there will have to be a guest API to handle the differences.

> SNP host code depends on CONFIG_KVM_AMD_SEV config flag, which may be
> enabled even when CONFIG_AMD_MEM_ENCRYPT isn't set, so update the
> SNP-specific IOMMU helpers used here to rely on CONFIG_KVM_AMD_SEV
> instead of CONFIG_AMD_MEM_ENCRYPT.

Does that mean that even on CONFIG_AMD_MEM_ENCRYPT=n kernels, host SNP
can function?

Do we even want that?

I'd expect that a host SNP kernel should have SME enabled too even
though it is not absolutely necessary.

> Co-developed-by: Ashish Kalra <ashish.kalra@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> Co-developed-by: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> [mdr: rework commit message to be clearer about what patch does, squash
> in early_rmptable_check() handling from Tom]
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
> arch/x86/coco/Makefile | 1 +
> arch/x86/coco/sev/Makefile | 3 +
> arch/x86/coco/sev/host.c | 212 +++++++++++++++++++++++
> arch/x86/include/asm/disabled-features.h | 8 +-
> arch/x86/include/asm/msr-index.h | 11 +-
> arch/x86/include/asm/sev.h | 2 +
> arch/x86/kernel/cpu/amd.c | 19 ++
> drivers/iommu/amd/init.c | 2 +-
> include/linux/amd-iommu.h | 2 +-
> 9 files changed, 256 insertions(+), 4 deletions(-)
> create mode 100644 arch/x86/coco/sev/Makefile
> create mode 100644 arch/x86/coco/sev/host.c

Ignored review comments here:

https://lore.kernel.org/r/Y9ubi0i4Z750gdMm@zn.tnic

Ignoring this one for now too.

--
Regards/Gruss,
Boris.