From dd9a14de35d2c4e308170ad2b51722d448d04e76 Mon Sep 17 00:00:00 2001 From: Laszlo Ersek Date: Thu, 27 Oct 2016 00:13:50 +0200 Subject: [PATCH] [librm] Conditionalize the workaround for the Tivoli VMM's SSE garbling MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Commit 71560d1 ("[librm] Preserve FPU, MMX and SSE state across calls to virt_call()") added FXSAVE and FXRSTOR instructions to iPXE. In KVM virtual machines, these instructions execute fine as long as the host CPU supports the "unrestricted_guest" feature (that is, it can virtualize big real mode natively). On older host CPUs however, KVM has to emulate big real mode, and it currently doesn't implement FXSAVE emulation. Upstream QEMU rebuilt iPXE at commit 0418631 ("[thunderx] Fix compilation with older versions of gcc") which is a descendant of commit 71560d1 (see above). This was done in QEMU commit ffdc5a2 ("ipxe: update submodule from 4e03af8ec to 041863191"). The resultant binaries were bundled with the QEMU v2.7.0 release; see QEMU commit c52125a ("ipxe: update prebuilt binaries"). This distributed the iPXE workaround for the Tivoli VMM bug to a number of KVM users with old host CPUs, causing KVM emulation failures (guest crashes) for them while netbooting. Make the FXSAVE and FXRSTOR instructions conditional on a new feature test macro called TIVOLI_VMM_WORKAROUND. Define the macro by default. There is prior art for an assembly file including config/general.h: see arch/x86/prefix/romprefix.S. Also, TIVOLI_VMM_WORKAROUND seems to be a good fit for the "Obscure configuration options" section in config/general.h. Cc: Bandan Das Cc: Gerd Hoffmann Cc: Greg Cc: Michael Brown Cc: Michael Prokop Cc: Paolo Bonzini Cc: Peter Pickford Cc: Radim Krčmář Ref: https://bugs.archlinux.org/task/50778 Ref: https://bugs.launchpad.net/qemu/+bug/1623276 Ref: https://bugzilla.proxmox.com/show_bug.cgi?id=1182 Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1356762 Signed-off-by: Laszlo Ersek Signed-off-by: Michael Brown --- src/arch/x86/transitions/librm.S | 16 ++++++++++++---- src/config/general.h | 3 +++ 2 files changed, 15 insertions(+), 4 deletions(-) diff --git a/src/arch/x86/transitions/librm.S b/src/arch/x86/transitions/librm.S index e91ede37..c31daad8 100644 --- a/src/arch/x86/transitions/librm.S +++ b/src/arch/x86/transitions/librm.S @@ -7,6 +7,9 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ) +/* Drag in general configuration */ +#include + /* Drag in local definitions */ #include "librm.h" @@ -207,7 +210,9 @@ VC_TMP_CR3: .space 4 VC_TMP_CR4: .space 4 VC_TMP_EMER: .space 8 .endif +#ifdef TIVOLI_VMM_WORKAROUND VC_TMP_FXSAVE: .space 512 +#endif VC_TMP_END: .previous @@ -1000,11 +1005,12 @@ virt_call: /* Claim ownership of temporary static buffer */ cli - - /* Preserve FPU, MMX and SSE state in temporary static buffer */ movw %cs:rm_ds, %ds - fxsave ( rm_tmpbuf + VC_TMP_FXSAVE ) +#ifdef TIVOLI_VMM_WORKAROUND + /* Preserve FPU, MMX and SSE state in temporary static buffer */ + fxsave ( rm_tmpbuf + VC_TMP_FXSAVE ) +#endif /* Preserve GDT and IDT in temporary static buffer */ sidt ( rm_tmpbuf + VC_TMP_IDT ) sgdt ( rm_tmpbuf + VC_TMP_GDT ) @@ -1070,9 +1076,11 @@ vc_rmode: movl $MSR_EFER, %ecx wrmsr .endif + +#ifdef TIVOLI_VMM_WORKAROUND /* Restore FPU, MMX and SSE state from temporary static buffer */ fxrstor ( rm_tmpbuf + VC_TMP_FXSAVE ) - +#endif /* Restore registers and flags and return */ popl %eax /* skip %cs and %ss */ popw %ds diff --git a/src/config/general.h b/src/config/general.h index d2bbeb06..be0845f6 100644 --- a/src/config/general.h +++ b/src/config/general.h @@ -190,6 +190,9 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); #undef GDBUDP /* Remote GDB debugging over UDP * (both may be set) */ //#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 */ #include #include NAMED_CONFIG(general.h)