From: Anton Ivanov <anton.iva...@cambridgegreys.com>
Preemption requires saving/restoring FPU state. This patch
adds support for it using GCC intrinsics.
Signed-off-by: Anton Ivanov <anton.iva...@cambridgegreys.com>
---
arch/um/Kconfig | 1 -
arch/um/Makefile | 3 +-
arch/um/include/asm/fpu/api.h | 4 +-
arch/um/include/asm/processor-generic.h | 3 +
arch/um/kernel/Makefile | 2 +-
arch/um/kernel/fpu.c | 83 +++++++++++++++++++++++++
arch/um/kernel/irq.c | 2 +
7 files changed, 93 insertions(+), 5 deletions(-)
create mode 100644 arch/um/kernel/fpu.c
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index b5e179360534..603f5fd82293 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -11,7 +11,6 @@ config UML
select ARCH_HAS_KCOV
select ARCH_HAS_STRNCPY_FROM_USER
select ARCH_HAS_STRNLEN_USER
- select ARCH_NO_PREEMPT
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_KASAN if X86_64
select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
diff --git a/arch/um/Makefile b/arch/um/Makefile
index 82f05f250634..6454f735cc9a 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -61,7 +61,8 @@ KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ \
$(ARCH_INCLUDE) $(MODE_INCLUDE) -Dvmap=kernel_vmap \
-Dlongjmp=kernel_longjmp -Dsetjmp=kernel_setjmp \
-Din6addr_loopback=kernel_in6addr_loopback \
- -Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr
+ -Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr \
+ -mxsave -mxsaveopt
KBUILD_RUSTFLAGS += -Crelocation-model=pie
diff --git a/arch/um/include/asm/fpu/api.h b/arch/um/include/asm/fpu/api.h
index 71bfd9ef3938..0094624ae9b4 100644
--- a/arch/um/include/asm/fpu/api.h
+++ b/arch/um/include/asm/fpu/api.h
@@ -8,8 +8,8 @@
* of x86 optimized copy, xor, etc routines into the
* UML code tree. */
-#define kernel_fpu_begin() (void)0
-#define kernel_fpu_end() (void)0
+void kernel_fpu_begin(void);
+void kernel_fpu_end(void);
static inline bool irq_fpu_usable(void)
{
diff --git a/arch/um/include/asm/processor-generic.h
b/arch/um/include/asm/processor-generic.h
index 7414154b8e9a..d5924d0e16a7 100644
--- a/arch/um/include/asm/processor-generic.h
+++ b/arch/um/include/asm/processor-generic.h
@@ -44,6 +44,9 @@ struct thread_struct {
} cb;
} u;
} request;
+#if defined(PREEMPT) || defined(PREEMPT_VOLUNTRARY)
+ u8 fpu[2048] __aligned(64); /* Intel docs require xsave/xrestore area to
be aligned to 16 bytes */
+#endif
};
#define INIT_THREAD \
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
index 811188be954c..5d9fbaa544be 100644
--- a/arch/um/kernel/Makefile
+++ b/arch/um/kernel/Makefile
@@ -16,7 +16,7 @@ extra-y := vmlinux.lds
obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
physmem.o process.o ptrace.o reboot.o sigio.o \
- signal.o sysrq.o time.o tlb.o trap.o \
+ signal.o sysrq.o time.o tlb.o trap.o fpu.o\
um_arch.o umid.o maccess.o kmsg_dump.o capflags.o skas/
obj-y += load_file.o
diff --git a/arch/um/kernel/fpu.c b/arch/um/kernel/fpu.c
new file mode 100644
index 000000000000..fb90da5a0227
--- /dev/null
+++ b/arch/um/kernel/fpu.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 Cambridge Greys Ltd
+ * Copyright (C) 2023 Red Hat Inc
+ */
+
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <asm/fpu/api.h>
+#include <asm/cpufeature.h>
+
+/*
+ * The critical section between kernel_fpu_begin() and kernel_fpu_end()
+ * is non-reentrant. It is the caller's responsibility to avoid reentrance.
+ */
+
+#if defined(PREEMPT) || defined(PREEMPT_VOLUNTRARY)
+static DEFINE_PER_CPU(bool, in_kernel_fpu);
+#endif
+
+/* UML knows about 387 features up to and including AVX512, tile, etc are not
yet
+ * supported.
+ */
+
+#define KNOWN_387_FEATURES 0xFF
+
+
+void kernel_fpu_begin(void)
+{
+#if defined(PREEMPT) || defined(PREEMPT_VOLUNTRARY)
+ preempt_disable();
+
+ WARN_ON(this_cpu_read(in_kernel_fpu));
+
+ this_cpu_write(in_kernel_fpu, true);
+
+#ifdef CONFIG_64BIT
+ if (likely(cpu_has(&boot_cpu_data, X86_FEATURE_XSAVEOPT)))
+ __builtin_ia32_xsaveopt64(¤t->thread.fpu,
KNOWN_387_FEATURES);
+ else {
+ if (cpu_has(&boot_cpu_data, X86_FEATURE_XSAVE))
+ __builtin_ia32_xsave64(¤t->thread.fpu,
KNOWN_387_FEATURES);
+ else
+ __builtin_ia32_fxsave64(¤t->thread.fpu);
+ }
+#else
+ if (likely(cpu_has(&boot_cpu_data, X86_FEATURE_XSAVEOPT)))
+ __builtin_ia32_xsaveopt(¤t->thread.fpu,
KNOWN_387_FEATURES);
+ else {
+ if (cpu_has(&boot_cpu_data, X86_FEATURE_XSAVE))
+ __builtin_ia32_xsave(¤t->thread.fpu,
KNOWN_387_FEATURES);
+ else
+ __builtin_ia32_fxsave(¤t->thread.fpu);
+ }
+#endif
+#endif
+}
+
+EXPORT_SYMBOL_GPL(kernel_fpu_begin);
+
+void kernel_fpu_end(void)
+{
+#if defined(PREEMPT) || defined(PREEMPT_VOLUNTRARY)
+ WARN_ON(!this_cpu_read(in_kernel_fpu));
+
+#ifdef CONFIG_64BIT
+ if (likely(cpu_has(&boot_cpu_data, X86_FEATURE_XSAVE)))
+ __builtin_ia32_xrstor64(¤t->thread.fpu,
KNOWN_387_FEATURES);
+ else
+ __builtin_ia32_fxrstor64(¤t->thread.fpu);
+#else
+ if (likely(cpu_has(&boot_cpu_data, X86_FEATURE_XSAVE)))
+ __builtin_ia32_xrstor(¤t->thread.fpu, KNOWN_387_FEATURES);
+ else
+ __builtin_ia32_fxrstor(¤t->thread.fpu);
+#endif
+ this_cpu_write(in_kernel_fpu, false);
+
+ preempt_enable();
+#endif
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_end);
+
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
index 635d44606bfe..c02525da45df 100644
--- a/arch/um/kernel/irq.c
+++ b/arch/um/kernel/irq.c
@@ -195,7 +195,9 @@ static void _sigio_handler(struct uml_pt_regs *regs,
void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs
*regs)
{
+ preempt_disable();
_sigio_handler(regs, irqs_suspended);
+ preempt_enable();
}
static struct irq_entry *get_irq_entry_by_fd(int fd)
--
2.30.2
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