Newer hardware offers more efficient and/or flexible and/or capable instructions, some of which we can make good use of in the hypervisor as well. Allow a basic way (no alternatives patching) of enabling their use. Of course this means that hypervisors thus built won't work anymore on older, less capable hardware.
Signed-off-by: Jan Beulich <[email protected]> --- TBD: Should we, just like for NX, add an early check in assembly code, to have a "clean" failure rather than a random crash? Whereas the baseline -> v2 step isn't much of a difference (we'll gain more there by a subsequent patch), v2 -> v3, while presumably (or shall I say hopefully) faster, yields an overall growth of .text size by (in my build) about 2k. The primary reason for this appear to be conversions of SHL-by-immediate to SHLX. --- a/xen/arch/x86/Kconfig +++ b/xen/arch/x86/Kconfig @@ -118,6 +118,36 @@ config HVM If unsure, say Y. +choice + prompt "base psABI level" + default X86_64_BASELINE + help + The psABI defines 4 levels of ISA extension sets as a coarse granular + way of identifying advanced functionality that would be uniformly + available in respectively newer hardware. While v4 is not really of + interest for Xen, the others can be selected here, making the + resulting Xen no longer work on older hardware. This option won't + have any effect if the toolchain doesn't support the distinction. + + If unsure, stick to the default. + +config X86_64_BASELINE + bool "baseline" + +config X86_64_V2 + bool "v2" + help + This enables POPCNT and CX16, besides other extensions which are of + no interest here. + +config X86_64_V3 + bool "v3" + help + This enables BMI, BMI2, LZCNT, and MOVBE, besides other extensions + which are of no interest here. + +endchoice + config XEN_SHSTK bool "Supervisor Shadow Stacks" depends on HAS_AS_CET_SS --- a/xen/arch/x86/arch.mk +++ b/xen/arch/x86/arch.mk @@ -36,6 +36,10 @@ CFLAGS += -mno-red-zone -fpic # the SSE setup for variadic function calls. CFLAGS += -mno-mmx -mno-sse $(call cc-option,$(CC),-mskip-rax-setup) +# Enable the selected baseline ABI, if supported by the compiler. +CFLAGS-$(CONFIG_X86_64_V2) += $(call cc-option,$(CC),-march=x86-64-v2) +CFLAGS-$(CONFIG_X86_64_V3) += $(call cc-option,$(CC),-march=x86-64-v3) + ifeq ($(CONFIG_INDIRECT_THUNK),y) # Compile with gcc thunk-extern, indirect-branch-register if available. CFLAGS-$(CONFIG_CC_IS_GCC) += -mindirect-branch=thunk-extern
