KVM: x86: Add dedicated storage for guest RIP

KVM: x86: Add dedicated storage for guest RIP

Add kvm_vcpu_arch.rip to track guest RIP instead of including it in the
generic regs[] array.  Decoupling RIP from regs[] will allow using a
*completely* arbitrary index for RIP, as opposed to the mostly-arbitrary
index that is currently used.  That in turn will allow using indices
16-31 to track R16-R31 that are coming with APX.

Note, although RIP can used for addressing, it does NOT have an
architecturally defined index, and so can't be reached via flows like
get_vmx_mem_address() where KVM "blindly" reads a general purpose register
given the SIB information reported by hardware.  For RIP-relative
addressing, hardware reports the full "offset" in vmcs.EXIT_QUALIFICATION.

Note #2, keep the available/dirty tracking as RSP is context switched
through the VMCS, i.e. needs to be cached for VMX.

Opportunistically rename NR_VCPU_REGS to NR_VCPU_GENERAL_PURPOSE_REGS to
better capture what it tracks, and so that KVM can slot in R16-R13 without
running into weirdness where KVM's definition of "EXREG" doesn't line up
with APX's definition of "extended reg".

No functional change intended.

Cc: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20260409224236.2021562-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>