Provide "nosnp" boot option via "sev=nosnp" kernel command line to
prevent SEV-SNP [1] capable host kernel from enabling SEV-SNP and
initializing Reverse Map Table (RMP)

Setting 'nosnp' avoids the RMP check overhead in memory accesses when
users do not want to run SEV-SNP guests.

On providing sev=nosnp via kernel command line:
cat /sys/module/kvm_amd/parameters/sev_snp should be "N".

The patchset is based on tip/master.

Reference:
[1] https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf

Changelog:
=========
v5:
  * Update cover-letter and Documentation to include information on why
    nosnp command line option is required (Dave Hansen)
  * Remove <asm/cache.h> stray header introduced in the previous
    versions because of __read_mostly attribute that is now moved into
    virt/svm/cmdline.c
  * Link: https://lore.kernel.org/all/20240930231102.123403-1-papaluri@amd.com/

v4:
  * Move __read_mostly attribute to place where sev_cfg is declared (Tom)
  * Link: https://lore.kernel.org/all/20240922033626.29038-1-papaluri@amd.com/

Pavan Kumar Paluri (2):
  x86, KVM:SVM: Move sev specific parsing into arch/x86/virt/svm
  x86 KVM:SVM: Provide "nosnp" boot option for sev kernel command line

 .../arch/x86/x86_64/boot-options.rst          |  5 +++
 arch/x86/coco/sev/core.c                      | 44 -------------------
 arch/x86/include/asm/sev-common.h             | 27 ++++++++++++
 arch/x86/virt/svm/Makefile                    |  1 +
 arch/x86/virt/svm/cmdline.c                   | 39 ++++++++++++++++
 5 files changed, 72 insertions(+), 44 deletions(-)
 create mode 100644 arch/x86/virt/svm/cmdline.c


base-commit: 00d91979d23c88d3f50870e22fc9cec3f5e26a2a
-- 
2.34.1