From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
commit 12209993e98c5fa1855c467f22a24e3d5b8be205 upstream.
There is one user of __kernel_fpu_begin() and before invoking it,
it invokes preempt_disable(). So it could invoke kernel_fpu_begin()
right away. The 32bit version of arch_efi_call_virt_setup() and
arch_efi_call_virt_teardown() does this already.
The comment above *kernel_fpu*() claims that before invoking
__kernel_fpu_begin() preemption should be disabled and that KVM is a
good example of doing it. Well, KVM doesn't do that since commit
f775b13eedee2 ("x86,kvm: move qemu/guest FPU switching out to vcpu_run")
so it is not an example anymore.
With EFI gone as the last user of __kernel_fpu_{begin|end}(), both can
be made static and not exported anymore.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Nicolai Stange <nstange@xxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kvm ML <kvm@xxxxxxxxxxxxxxx>
Cc: linux-efi <linux-efi@xxxxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20181129150210.2k4mawt37ow6c2vq@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/efi.h | 6 ++----
arch/x86/include/asm/fpu/api.h | 15 +++++----------
arch/x86/kernel/fpu/core.c | 6 ++----
3 files changed, 9 insertions(+), 18 deletions(-)
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -82,8 +82,7 @@ struct efi_scratch {
#define arch_efi_call_virt_setup() \
({ \
efi_sync_low_kernel_mappings(); \
- preempt_disable(); \
- __kernel_fpu_begin(); \
+ kernel_fpu_begin(); \
firmware_restrict_branch_speculation_start(); \
\
if (!efi_enabled(EFI_OLD_MEMMAP)) \
@@ -99,8 +98,7 @@ struct efi_scratch {
efi_switch_mm(efi_scratch.prev_mm); \
\
firmware_restrict_branch_speculation_end(); \
- __kernel_fpu_end(); \
- preempt_enable(); \
+ kernel_fpu_end(); \
})
extern void __iomem *__init efi_ioremap(unsigned long addr, unsigned long size,
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -12,17 +12,12 @@
#define _ASM_X86_FPU_API_H
/*
- * Careful: __kernel_fpu_begin/end() must be called with preempt disabled
- * and they don't touch the preempt state on their own.
- * If you enable preemption after __kernel_fpu_begin(), preempt notifier
- * should call the __kernel_fpu_end() to prevent the kernel/user FPU
- * state from getting corrupted. KVM for example uses this model.
- *
- * All other cases use kernel_fpu_begin/end() which disable preemption
- * during kernel FPU usage.
+ * Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It
+ * disables preemption so be careful if you intend to use it for long periods
+ * of time.
+ * If you intend to use the FPU in softirq you need to check first with
+ * irq_fpu_usable() if it is possible.
*/
-extern void __kernel_fpu_begin(void);
-extern void __kernel_fpu_end(void);
extern void kernel_fpu_begin(void);
extern void kernel_fpu_end(void);
extern bool irq_fpu_usable(void);
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -93,7 +93,7 @@ bool irq_fpu_usable(void)
}
EXPORT_SYMBOL(irq_fpu_usable);
-void __kernel_fpu_begin(void)
+static void __kernel_fpu_begin(void)
{
struct fpu *fpu = ¤t->thread.fpu;
@@ -111,9 +111,8 @@ void __kernel_fpu_begin(void)
__cpu_invalidate_fpregs_state();
}
}
-EXPORT_SYMBOL(__kernel_fpu_begin);
-void __kernel_fpu_end(void)
+static void __kernel_fpu_end(void)
{
struct fpu *fpu = ¤t->thread.fpu;
@@ -122,7 +121,6 @@ void __kernel_fpu_end(void)
kernel_fpu_enable();
}
-EXPORT_SYMBOL(__kernel_fpu_end);
void kernel_fpu_begin(void)
{
