[PATCH 0/9] Linear Address Masking (LAM) KVM Enabling

Robert Hoo
2022-10-17T07:05:37Z

===Feature Introduction===

Linear-address masking (LAM) [1], modifies the checking that is applied to
*64-bit* linear addresses, allowing software to use of the untranslated
address (upper) bits for metadata.
As for which upper bits of linear address can be borrowed, LAM has 2 modes:
LAM_48 (bits 62:48, i.e. LAM width of 15) and LAM_57 (bits 62:57, i.e. LAM
width of 6), controlled by these new bits: CR3[62] (LAM_U48), CR3[61]
(LAM_U57), and CR4[28] (LAM_SUP).

* LAM_U48 and LAM_U57 bits controls LAM for user mode address. I.e. if
CR3.LAM_U57 = 1, LAM57 is applied; if CR3.LAM_U48 = 1 and CR3.LAM_U57 = 0,
LAM48 is applied.
* LAM_SUP bit, combined with paging mode (4-level or 5-level), determines
LAM status for supervisor mode address. I.e. when CR4.LAM_SUP =1, 4-level
paging mode will have LAM48 for supervisor mode address while 5-level paging
will have LAM57.

Note:
1. LAM applies to only data address, not to instructions.
2. LAM identification of an address as user or supervisor is based solely on the
value of pointer bit 63 and does not, for the purposes of LAM, depend on the CPL.
3. For user mode address, it is possible that 5-level paging and LAM_U48 are both
set, in this case, the effective usable linear address width is 48, i.e. bit
56:47 is reserved by LAM. [2]

===LAM KVM Design===

Pass CR4.LAM_SUP under guest control.

Under EPT mode, CR3 is fully under guest control, guest LAM is thus transparent to
KVM. Nothing more need to do.

For Shadow paging (EPT = off), KVM need to handle guest CR3.LAM_U48 and CR3.LAM_U57
toggles.

Patch 1 -- This patch can be mostly independent from LAM enabling. It just renames
CR4 reserved bits for better understanding, esp. for beginners.

Patch 2, 9 -- Common part for both EPT and Shadow Paging modes enabling.

Patch 3 ~ 8 -- For Shadow Paging mode LAM enabling.

This patch set is based on Kirill's up-to-date LAM Kernel enabling
(e3e52d2898d66c34eefbe09cbeae0d3ba53fb989)
https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git lam

Unit tested with self test tools in both host and VM, passed.

[1] ISE Chap10 https://cdrdv2.intel.com/v1/dl/getContent/671368 (Section 10.6 VMX interaction)
[2] Thus currently, Kernel enabling patch only enables LAM57 mode. https://lore.kernel.org/lkml/20220815041803.17954-1-kirill.shutemov@linux.intel.com/

Robert Hoo (9):
KVM: x86: Rename cr4_reserved/rsvd_* variables to be more readable
KVM: x86: Add CR4.LAM_SUP in guest owned bits
KVM: x86: MMU: Rename get_cr3() --> get_pgd() and clear high bits for
pgd
[Trivial] KVM: x86: MMU: Commets update
KVM: x86: MMU: Integrate LAM bits when build guest CR3
KVM: x86: Untag LAM bits when applicable
KVM: x86: When judging setting CR3 valid or not, consider LAM bits
KVM: x86: When guest set CR3, handle LAM bits semantics
KVM: x86: LAM: Expose LAM CPUID to user space VMM

arch/x86/include/asm/kvm_host.h | 7 ++--
arch/x86/include/asm/processor-flags.h | 1 +
arch/x86/kvm/cpuid.c | 6 +--
arch/x86/kvm/kvm_cache_regs.h | 3 +-
arch/x86/kvm/mmu.h | 5 +++
arch/x86/kvm/mmu/mmu.c | 16 +++++---
arch/x86/kvm/vmx/vmx.c | 8 +++-
arch/x86/kvm/x86.c | 53 ++++++++++++++++++++------
arch/x86/kvm/x86.h | 43 ++++++++++++++++++++-
9 files changed, 114 insertions(+), 28 deletions(-)

--
2.31.1