On 3/2/2023 4:55 PM, Chao Gao wrote:
On Mon, Feb 27, 2023 at 04:45:46PM +0800, Robert Hoo wrote:Emulate HW LAM masking when doing data access under 64-bit mode. kvm_lam_untag_addr() implements this: per CR4/CR3 LAM bits configuration, firstly check the linear addr conforms LAM canonical, i.e. the highest address bit matches bit 63. Then mask out meta data per LAM configuration. If failed in above process, emulate #GP to guest. Signed-off-by: Robert Hoo <robert.hu@xxxxxxxxxxxxxxx> --- arch/x86/kvm/emulate.c | 13 ++++++++ arch/x86/kvm/x86.h | 70 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 83 insertions(+) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 5cc3efa0e21c..77bd13f40711 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -700,6 +700,19 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt, *max_size = 0; switch (mode) { case X86EMUL_MODE_PROT64: + /* LAM applies only on data access */ + if (!fetch && guest_cpuid_has(ctxt->vcpu, X86_FEATURE_LAM)) { + enum lam_type type; + + type = kvm_vcpu_lam_type(la, ctxt->vcpu); + if (type == LAM_ILLEGAL) { + *linear = la; + goto bad; + } else { + la = kvm_lam_untag_addr(la, type); + } + } + *linear = la; va_bits = ctxt_virt_addr_bits(ctxt); if (!__is_canonical_address(la, va_bits))...+static inline u64 kvm_lam_untag_addr(u64 addr, enum lam_type type) +{ + switch (type) { + case LAM_U57: + case LAM_S57: + addr = __canonical_address(addr, 57); + break; + case LAM_U48: + case LAM_S48: + addr = __canonical_address(addr, 48); + break; + case LAM_NONE: + default: + break; + } + + return addr; +}LAM's change to canonicality check is: before performing the check, software metadata in pointers is masked by sign-extending the value of bit 56/47. so, to emulate this behavior, in kvm_lam_untag_addr(), we can simply: 1. determine which LAM configuration is enabled, LAM57 or LAM48. 2. mask software metadata by sign-extending the bit56/47, i.e., addr = (sign_extern64(addr, X) & ~BIT_ULL(63)) | (addr & BIT_ULL(63)); where X=56 for LAM57 and X=47 for LAM48. Note that this doesn't ensure the resulting @addr is canonical. It isn't a problem because the original canonicality check (__is_canonical_address() above) can identify non-canonical addresses and raise #GP/#SS to the guest.
Thanks for your suggestion. It's much simpler.
