On Fri, Dec 09, 2022 at 12:45:48PM +0800, Robert Hoo wrote: > ===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] It's worth to higlight that vmx exit Guest Linear Address field is always filled without the LAM metadata part, it can be used as linear address directly. I think this explains reason of no modification on paging_tmpl.h for shadow paging. > > > ===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. > > [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@xxxxxxxxxxxxxxx/ > > --- > Changelog > v2 --> v3: > As LAM Kernel patches are in tip tree now, rebase to it. > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/ > > v1 --> v2: > 1. Fixes i386-allyesconfig build error on get_pgd(), where > CR3_HIGH_RSVD_MASK isn't applicable. > (Reported-by: kernel test robot <lkp@xxxxxxxxx>) > 2. In kvm_set_cr3(), be conservative on skip tlb flush when only LAM bits > toggles. (Kirill) > > 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 > 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 | 18 ++++++--- > arch/x86/kvm/vmx/vmx.c | 8 +++- > arch/x86/kvm/x86.c | 51 ++++++++++++++++++++------ > arch/x86/kvm/x86.h | 43 +++++++++++++++++++++- > 9 files changed, 115 insertions(+), 27 deletions(-) > > > base-commit: a5dadcb601b4954c60494d797b4dd1e03a4b1ebe > -- > 2.31.1 >
