On 2/24/2025 8:27 PM, Adrian Hunter wrote:
On 20/02/25 15:16, Xiaoyao Li wrote:
On 1/29/2025 5:58 PM, Adrian Hunter wrote:
+#define TDX_REGS_UNSUPPORTED_SET (BIT(VCPU_EXREG_RFLAGS) | \
+ BIT(VCPU_EXREG_SEGMENTS))
+
+fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
+{
+ /*
+ * force_immediate_exit requires vCPU entering for events injection with
+ * an immediately exit followed. But The TDX module doesn't guarantee
+ * entry, it's already possible for KVM to_think_ it completely entry
+ * to the guest without actually having done so.
+ * Since KVM never needs to force an immediate exit for TDX, and can't
+ * do direct injection, just warn on force_immediate_exit.
+ */
+ WARN_ON_ONCE(force_immediate_exit);
+
+ trace_kvm_entry(vcpu, force_immediate_exit);
+
+ tdx_vcpu_enter_exit(vcpu);
+
+ vcpu->arch.regs_avail &= ~TDX_REGS_UNSUPPORTED_SET;
I don't understand this. Why only clear RFLAGS and SEGMENTS?
When creating the vcpu, vcpu->arch.regs_avail = ~0 in kvm_arch_vcpu_create().
now it only clears RFLAGS and SEGMENTS for TDX vcpu, which leaves other bits set. But I don't see any code that syncs the guest value of into vcpu->arch.regs[reg].
TDX guest registers are generally not known but
values are placed into vcpu->arch.regs when needed
to work with common code.
We used to use ~VMX_REGS_LAZY_LOAD_SET and tdx_cache_reg()
which has since been removed.
tdx_cache_reg() did not support RFLAGS, SEGMENTS,
EXIT_INFO_1/EXIT_INFO_2 but EXIT_INFO_1/EXIT_INFO_2 became
needed, so that just left RFLAGS, SEGMENTS.
Quote what Sean said [1]
“I'm also not convinced letting KVM read garbage for RIP, RSP, CR3, or
PDPTRs is at all reasonable. CR3 and PDPTRs should be unreachable,
and I gotta imagine the same holds true for RSP. Allow reads/writes
to RIP is fine, in that it probably simplifies the overall code.”
We need to justify why to let KVM read "garbage" of VCPU_REGS_RIP,
VCPU_EXREG_PDPTR, VCPU_EXREG_CR0, VCPU_EXREG_CR3, VCPU_EXREG_CR4,
VCPU_EXREG_EXIT_INFO_1, and VCPU_EXREG_EXIT_INFO_2 are neeed.
The changelog justify nothing for it.
btw, how EXIT_INFO_1/EXIT_INFO_2 became needed? It seems I cannot find
any TDX code use them.
[1] https://lore.kernel.org/all/Z2GiQS_RmYeHU09L@xxxxxxxxxx/
+ trace_kvm_exit(vcpu, KVM_ISA_VMX);
+
+ return EXIT_FASTPATH_NONE;
+}
