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Wed, 13 Jun 2018 14:05:43 -0700 (PDT) From: Nick Desaulniers To: akpm@linux-foundation.org, hpa@zytor.com, mingo@redhat.com, tglx@linutronix.de Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux-foundation.org, astrachan@google.com, manojgupta@google.com, ghackmann@google.com, sedat.dilek@gmail.com, tstellar@redhat.com, keescook@google.com, yamada.masahiro@socionext.com, michal.lkml@markovi.net, linux-kbuild@vger.kernel.org, geert@linux-m68k.org, will.deacon@arm.com, mawilcox@microsoft.com, arnd@arndb.de, rientjes@google.com, acme@redhat.com, pombredanne@nexb.com, aryabinin@virtuozzo.com, kstewart@linuxfoundation.org, boris.ostrovsky@oracle.com, jan.kiszka@siemens.com, rostedt@goodmis.org, kirill.shutemov@linux.intel.com, ard.biesheuvel@linaro.org, akataria@vmware.com, brijesh.singh@amd.com, caoj.fnst@cn.fujitsu.com, gregkh@linuxfoundation.org, jarkko.sakkinen@linux.intel.com, jgross@suse.com, jpoimboe@redhat.com, mka@chromium.org, ndesaulniers@google.com, thomas.lendacky@amd.com, tweek@google.com, mjg59@google.com, joe@perches.com, andrea.parri@amarulasolutions.com Subject: [PATCH v5 3/3] x86: paravirt: make native_save_fl extern inline Date: Wed, 13 Jun 2018 14:05:18 -0700 Message-Id: <20180613210518.113983-4-ndesaulniers@google.com> X-Mailer: git-send-email 2.18.0.rc1.244.gcf134e6275-goog In-Reply-To: <20180613210518.113983-1-ndesaulniers@google.com> References: <20180613210518.113983-1-ndesaulniers@google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org native_save_fl() is marked static inline, but by using it as a function pointer in arch/x86/kernel/paravirt.c, it MUST be outlined. paravirt's use of native_save_fl() also requires that no GPRs other than %rax are clobbered. Compilers have different heuristics which they use to emit stack guard code, the emittance of which can break paravirt's callee saved assumption by clobbering %rcx. Marking a function definition extern inline means that if this version cannot be inlined, then the out-of-line version will be preferred. By having the out-of-line version be implemented in assembly, it cannot be instrumented with a stack protector, which might violate custom calling conventions that code like paravirt rely on. The semantics of extern inline has changed since gnu89. This means that folks using GCC versions >= 5.1 may see symbol redefinition errors at link time for subdirs that override KBUILD_CFLAGS (making the C standard used implicit) regardless of this patch. This has been cleaned up earlier in the patch set, but is left as a note in the commit message for future travelers. Reports: https://lkml.org/lkml/2018/5/7/534 https://github.com/ClangBuiltLinux/linux/issues/16 Discussion: https://bugs.llvm.org/show_bug.cgi?id=37512 https://lkml.org/lkml/2018/5/24/1371 Thanks to the many folks that participated in the discussion. Debugged-by: Alistair Strachan Debugged-by: Matthias Kaehlcke Reported-by: Sedat Dilek Signed-off-by: Nick Desaulniers Suggested-by: Arnd Bergmann Suggested-by: H. Peter Anvin Suggested-by: Tom Stellar Tested-by: Sedat Dilek --- arch/x86/include/asm/irqflags.h | 2 +- arch/x86/kernel/Makefile | 1 + arch/x86/kernel/irqflags.S | 26 ++++++++++++++++++++++++++ 3 files changed, 28 insertions(+), 1 deletion(-) create mode 100644 arch/x86/kernel/irqflags.S diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h index 89f08955fff7..c4fc17220df9 100644 --- a/arch/x86/include/asm/irqflags.h +++ b/arch/x86/include/asm/irqflags.h @@ -13,7 +13,7 @@ * Interrupt control: */ -static inline unsigned long native_save_fl(void) +extern inline unsigned long native_save_fl(void) { unsigned long flags; diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 02d6f5cf4e70..8824d01c0c35 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -61,6 +61,7 @@ obj-y += alternative.o i8253.o hw_breakpoint.o obj-y += tsc.o tsc_msr.o io_delay.o rtc.o obj-y += pci-iommu_table.o obj-y += resource.o +obj-y += irqflags.o obj-y += process.o obj-y += fpu/ diff --git a/arch/x86/kernel/irqflags.S b/arch/x86/kernel/irqflags.S new file mode 100644 index 000000000000..ddeeaac8adda --- /dev/null +++ b/arch/x86/kernel/irqflags.S @@ -0,0 +1,26 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include +#include +#include + +/* + * unsigned long native_save_fl(void) + */ +ENTRY(native_save_fl) + pushf + pop %_ASM_AX + ret +ENDPROC(native_save_fl) +EXPORT_SYMBOL(native_save_fl) + +/* + * void native_restore_fl(unsigned long flags) + * %eax/%rdi: flags + */ +ENTRY(native_restore_fl) + push %_ASM_ARG1 + popf + ret +ENDPROC(native_restore_fl) +EXPORT_SYMBOL(native_restore_fl) -- 2.18.0.rc1.244.gcf134e6275-goog