[librm] Remove conditionalisation of the Tivoli VMM workaround

Commit 71560d1 ("[librm] Preserve FPU, MMX and SSE state across calls
to virt_call()") originally introduced the use of "fxsave" and
"fxrstor" to work around a bug in the implementation of memcpy()
within the IBM Tivoli Provisioning Manager's VMM.  This commit assumed
(with justification given in the commit message) that SSE support
could be assumed to be present on any realistic in-scope CPU, and so
these instructions may safely be assumed to be supported.

Commit dd9a14d ("[librm] Conditionalize the workaround for the Tivoli
VMM's SSE garbling") then made this workaround a compile-time
conditional, to work around a missing feature in QEMU that caused the
use of "fxsave" and "fxrstor" to fail in QEMU VMs on some host CPUs.

Commit 900f1f9 ("[librm] Test for FXSAVE/FXRSTOR instruction support")
then added a runtime CPUID check for the FXSR feature, to allow the
unmodified iPXE binary to be used on older CPUs.

Supporting AES hardware acceleration via AES-NI will require setting
the CR4.OSFXSR control bit, which in turn must be conditionalised upon
the same runtime CPUID check for the FXSR feature.

Perform the runtime check unconditionally, and assume that we no
longer need the compile-time conditional (i.e. assume either that
newer versions of QEMU emulate "fxsave" and "fxrstor" when needed, or
that QEMU reports via CPUID that FXSR is not supported if it cannot
support those instructions).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/transitions/librm.S

@@ -349,12 +349,10 @@ init_librm_rmode:
 	/* Initialise IDT */
 	virtcall init_idt
 
-#ifdef TIVOLI_VMM_WORKAROUND
 	/* Check for FXSAVE/FXRSTOR */
 	clc
 	virtcall check_fxsr
 	setnc	fxsr_supported
-#endif
 
 	/* Restore registers */
 	popl	%edi

src/config/general.h

@@ -303,9 +303,6 @@ FILE_SECBOOT ( PERMITTED );
 //#define GDBSERIAL		/* Remote GDB debugging over serial */
 //#define GDBUDP		/* Remote GDB debugging over UDP */
 //#define EFI_DOWNGRADE_UX	/* Downgrade UEFI user experience */
-#define TIVOLI_VMM_WORKAROUND	/* Work around the Tivoli VMM's garbling of SSE
-				 * registers when iPXE traps to it due to
-				 * privileged instructions */
 //#define ERRMSG_80211		/* All 802.11 error descriptions (~3.3kb) */
 
 #include <config/named.h>

src/config/qemu/general.h

@@ -8,8 +8,3 @@
 
 /* Work around missing EFI_PXE_BASE_CODE_PROTOCOL */
 #define EFI_DOWNGRADE_UX
-
-/* The Tivoli VMM workaround causes a KVM emulation failure on hosts
- * without unrestricted_guest support
- */
-#undef TIVOLI_VMM_WORKAROUND