Re: [PATCH v8 0/6] Linear Address Masking (LAM) KVM Enabling

[Binbin Wu]

Gentle ping.
Do you have any comments for this patch series?

Thanks.

On 5/10/2023 2:06 PM, Binbin Wu 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
> bits for metadata and masks the metadata bits before using them as linear
> addresses to access memory.
>
> When the feature is virtualized and exposed to guest, it can be used for efficient
> address sanitizers (ASAN) implementation and for optimizations in JITs and virtual
> machines.
>
> Regarding which pointer bits are masked and can be used for metadata, LAM has 2
> modes:
> - LAM_48: metadata bits 62:48, i.e. LAM width of 15.
> - LAM_57: metadata bits 62:57, i.e. LAM width of 6.
>
> * For user pointers:
>    CR3.LAM_U57 = CR3.LAM_U48 = 0, LAM is off;
>    CR3.LAM_U57 = 1, LAM57 is active;
>    CR3.LAM_U57 = 0 and CR3.LAM_U48 = 1, LAM48 is active.
> * For supervisor pointers:
>    CR4.LAM_SUP =0, LAM is off;
>    CR4.LAM_SUP =1 with 5-level paging mode, LAM57 is active;
>    CR4.LAM_SUP =1 with 4-level paging mode, LAM48 is active.
>
> The modified LAM canonicality check:
> * LAM_S48                : [ 1 ][ metadata ][ 1 ]
>                               63               47
> * LAM_U48                : [ 0 ][ metadata ][ 0 ]
>                               63               47
> * LAM_S57                : [ 1 ][ metadata ][ 1 ]
>                               63               56
> * LAM_U57 + 5-lvl paging : [ 0 ][ metadata ][ 0 ]
>                               63               56
> * LAM_U57 + 4-lvl paging : [ 0 ][ metadata ][ 0...0 ]
>                               63               56..47
>
> 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 depend on the CPL.
> 3. LAM doesn't apply to the writes to control registers or MSRs.
> 4. LAM masking applies before paging, so the faulting linear address in CR2
>     doesn't contain the metadata.
> 5  The guest linear address saved in VMCS doesn't contain metadata.
> 6. 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.
>     (Currently, only LAM_U57 is enabled in Linux kernel. [2])
>
> ===LAM KVM Design===
> LAM KVM enabling includes the following parts:
> - Feature Enumeration
>    LAM feature is enumerated by CPUID.7.1:EAX.LAM[bit 26].
>    If hardware supports LAM and host doesn't disable it explicitly (e.g. via
>    clearcpuid), LAM feature will be exposed to user VMM.
>
> - CR4 Virtualization
>    LAM uses CR4.LAM_SUP (bit 28) to configure LAM on supervisor pointers.
>    Add support to allow guests to set the new CR4 control bit for guests to enable
>    LAM on supervisor pointers.
>
> - CR3 Virtualization
>    LAM uses CR3.LAM_U48 (bit 62) and CR3.LAM_U57 (bit 61) to configure LAM on user
>    pointers.
>    Add support to allow guests to set two new CR3 non-address control bits for
>    guests to enable LAM on user pointers.
>
> - Modified Canonicality Check and Metadata Mask
>    When LAM is enabled, 64-bit linear address may be tagged with metadata. Linear
>    address should be checked for modified canonicality and untagged in instruction
>    emulations and VMExit handlers when LAM is applicable.
>
> LAM inside nested guest is supported by this patch series.
> LAM inside SGX enclave mode is NOT supported by this patch series.
>
> LAM QEMU patch:
> https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg08036.html
>
> LAM kvm-unit-tests patch:
> https://lore.kernel.org/kvm/20230504084751.968-1-binbin.wu@xxxxxxxxxxxxxxx/
>
> ===Test===
> 1. Add test cases in kvm-unit-test [3] for LAM, including LAM_SUP and LAM_{U57,U48}.
>     For supervisor pointers, the test covers CR4 LAM_SUP bits toggle, Memory/MMIO
>     access with tagged pointer, and some special instructions (INVLPG, INVPCID,
>     INVVPID), INVVPID cases also used to cover VMX instruction VMExit path.
>     For uer pointers, the test covers CR3 LAM bits toggle, Memory/MMIO access with
>     tagged pointer.
>     MMIO cases are used to trigger instruction emulation path.
>     Run the unit test with both LAM feature on/off (i.e. including negative cases).
>     Run the unit test in L1 guest with both LAM feature on/off.
> 2. Run Kernel LAM kselftests [2] in guest, with both EPT=Y/N.
> 3. Launch a nested guest.
>
> All tests have passed in Simics environment.
>
> [1] Intel ISE https://cdrdv2.intel.com/v1/dl/getContent/671368
>      Chapter Linear Address Masking (LAM)
> [2] https://lore.kernel.org/all/20230312112612.31869-9-kirill.shutemov@xxxxxxxxxxxxxxx/
> [3] https://lore.kernel.org/kvm/20230504084751.968-1-binbin.wu@xxxxxxxxxxxxxxx/
>
> ---
> Changelog
> v7 --> v8:
> - Rebase the patch series on Linux kernel v6.4-rc1, which has all dependencies
>    of this patch series.
> - Add a cleanup patch to consolidate flags for __linearize().
> - Some changes in commit message of patch 2.
> - Rewrite the commit message of patch 3 (Thanks Kai Huang for the suggestion).
>    Opportunistically use GENMASK_ULL() to define __PT_BASE_ADDR_MASK.
>    Opportunistically use kvm_vcpu_is_legal_cr3() to check CR3 in SVM nested code,
>    to provide a clear distinction b/t CR3 and GPA checks.
> - Change interface untag_addr() to optional version to avoid adding a dummy
>    version in SVM in patch 4.
> - Verified and confirmed that LAM doesn't apply to the address in descriptor of
>    invvpid, drop the untag action for it in patch 5.
>
> v6 --> v7:
> - Changes to CR3 virtualization when EPT off
>    * Leave LAM bits in root.pgd to force a new root for a CR3+LAM combination. (Sean)
>    * Perform GFN calculation from guest CR3/PGD generically by extracting the maximal
>      base address mask. (Sean)
> - Remove de-reference of ctxt->vcpu in the emulator. (Sean)
> - Fix a bug in v6, which hardcoded "write" to "false" by mistake in linearize(). (Chao Gao)
> - Add Chao Gao's reviewed-by in Patch 5.
> - Add Xuelian Guo's tested-by in the patch set.
> - Separate cleanup patches from the patch set.
>
> v5 --> v6:
> Add Patch 2 to fix the check of 64-bit mode.
> Add untag_addr() to kvm_x86_ops to hide vendor specific code.
> Simplify the LAM canonicality check per Chao's suggestion.
> Add cr3_ctrl_bits to kvm_vcpu_arch to simplify cr3 invalidation/extract/mask (Chao Gao)
> Extend the patchset scope to include nested virtualization and SGX ENCLS handling.
> - Add X86_CR4_LAM_SUP in cr4_fixed1_update for nested vmx. (Chao Gao)
> - Add SGX ENCLS VMExit handling
> - Add VMX instruction VMExit handling
> More descriptions in cover letter.
> Add Chao's reviewed-by on Patch 4.
> Add more test cases in kvm-unit-test.
>
> v4 --> v5:
> Reorder and melt patches surround CR3.LAM bits into Patch 3 of this
> version.
> Revise Patch 1's subject and description
> Drop Patch 3
> Use kvm_read_cr4_bits() instead of kvm_read_cr4()
> Fix: No need to untag addr when write to msr, it should be legacy canonical check
> Rename kvm_is_valid_cr3() --> kvm_vcpu_is_valid_cr3(), and update some call
> sites of kvm_vcpu_is_valid_cr3() to use kvm_is_valid_cr3().
> Other refactors and Miscs.
>
> v3 --> v4:
> Drop unrelated Patch 1 in v3 (Binbin, Sean, Xiaoyao)
> Intercept CR4.LAM_SUP instead of pass through to guest (Sean)
> Just filter out CR3.LAM_{U48, U57}, instead of all reserved high bits
> (Sean, Yuan)
> Use existing __canonical_address() helper instead write a new one (Weijiang)
> Add LAM handling in KVM emulation (Yu, Yuan)
> Add Jingqi's reviwed-by on Patch 7
> Rebased to Kirill's latest code, which is 6.2-rc1 base.
>
> 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)
>
> Binbin Wu (3):
>    KVM: x86: Consolidate flags for __linearize()
>    KVM: x86: Introduce untag_addr() in kvm_x86_ops
>    KVM: x86: Untag address when LAM applicable
>
> Robert Hoo (3):
>    KVM: x86: Virtualize CR4.LAM_SUP
>    KVM: x86: Virtualize CR3.LAM_{U48,U57}
>    KVM: x86: Expose LAM feature to userspace VMM
>
>   arch/x86/include/asm/kvm-x86-ops.h |  1 +
>   arch/x86/include/asm/kvm_host.h    | 10 ++++-
>   arch/x86/kvm/cpuid.c               |  2 +-
>   arch/x86/kvm/cpuid.h               |  5 +++
>   arch/x86/kvm/emulate.c             | 30 +++++++++++----
>   arch/x86/kvm/kvm_emulate.h         |  7 ++++
>   arch/x86/kvm/mmu.h                 |  5 +++
>   arch/x86/kvm/mmu/mmu.c             |  8 +++-
>   arch/x86/kvm/mmu/mmu_internal.h    |  1 +
>   arch/x86/kvm/mmu/paging_tmpl.h     |  3 +-
>   arch/x86/kvm/mmu/spte.h            |  2 +-
>   arch/x86/kvm/svm/nested.c          |  4 +-
>   arch/x86/kvm/vmx/nested.c          |  6 ++-
>   arch/x86/kvm/vmx/sgx.c             |  1 +
>   arch/x86/kvm/vmx/vmx.c             | 59 +++++++++++++++++++++++++++++-
>   arch/x86/kvm/vmx/vmx.h             |  2 +
>   arch/x86/kvm/x86.c                 | 11 +++++-
>   arch/x86/kvm/x86.h                 |  2 +
>   18 files changed, 140 insertions(+), 19 deletions(-)
>
>
> base-commit: ac9a78681b921877518763ba0e89202254349d1b