| Message ID | 20190109114744.10936-16-bigeasy@linutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v6] x86: load FPU registers on return to userland | expand |
On Wed, Jan 09, 2019 at 12:47:37PM +0100, Sebastian Andrzej Siewior wrote: > Add TIF_NEED_FPU_LOAD. This is reserved for loading the FPU registers > before returning to userland. This flag must not be set for systems > without a FPU. > If this flag is cleared, the CPU's FPU register hold the current content > of current()'s FPU register. The in-memory copy (union fpregs_state) is > not valid. > If this flag is set, then all of CPU's FPU register may hold a random > value (except for PKRU) and it is required to load the content of the > FPU register on return to userland. This definitely needs to be written somewhere in arch/x86/include/asm/fpu/internal.h or where we decide to put the FPU handling rules.
On 2019-01-30 12:55:07 [+0100], Borislav Petkov wrote: > This definitely needs to be written somewhere in > > arch/x86/include/asm/fpu/internal.h > > or where we decide to put the FPU handling rules. Added: Index: staging/arch/x86/include/asm/fpu/internal.h =================================================================== --- staging.orig/arch/x86/include/asm/fpu/internal.h +++ staging/arch/x86/include/asm/fpu/internal.h @@ -537,6 +537,12 @@ static inline void __fpregs_load_activat * * The FPU context is only stored/restore for user task and ->mm is used to * distinguish between kernel and user threads. + * + * If TIF_NEED_FPU_LOAD is cleared then CPU's FPU registers are holding the + * current content of current()'s FPU register state. + * If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not hold current()'s + * FPU registers. It is required to load the register before returning to + * userland or using the content otherwise. */ static inline void switch_fpu_prepare(struct fpu *old_fpu, int cpu) Sebastian
On Thu, Feb 07, 2019 at 12:49:42PM +0100, Sebastian Andrzej Siewior wrote: > On 2019-01-30 12:55:07 [+0100], Borislav Petkov wrote: > > This definitely needs to be written somewhere in > > > > arch/x86/include/asm/fpu/internal.h > > > > or where we decide to put the FPU handling rules. > > Added: > > Index: staging/arch/x86/include/asm/fpu/internal.h > =================================================================== > --- staging.orig/arch/x86/include/asm/fpu/internal.h > +++ staging/arch/x86/include/asm/fpu/internal.h > @@ -537,6 +537,12 @@ static inline void __fpregs_load_activat > * > * The FPU context is only stored/restore for user task and ->mm is used to > * distinguish between kernel and user threads. > + * > + * If TIF_NEED_FPU_LOAD is cleared then CPU's FPU registers are holding the > + * current content of current()'s FPU register state. "current content of current" - that's a lot of c... Make that "... then the CPU's FPU registers are mirrored in the current thread's FPU registers state." > + * If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not hold current()'s > + * FPU registers. It is required to load the register before returning to ^^^^^^^^ s/register/registers/ - plural. Thx.
On 2019-02-13 10:35:53 [+0100], Borislav Petkov wrote: … > > + * > > + * If TIF_NEED_FPU_LOAD is cleared then CPU's FPU registers are holding the > > + * current content of current()'s FPU register state. > > "current content of current" - that's a lot of c... > > Make that > > "... then the CPU's FPU registers are mirrored in the current thread's > FPU registers state." Replaced `mirrored' with saved: + * If TIF_NEED_FPU_LOAD is cleared then the CPU's FPU registers are saved in + * the current thread's FPU registers state. + * If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not hold current()'s + * FPU registers. It is required to load the registers before returning to + * userland or using the content otherwise. Sebastian
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index e0eccbcb8447d..f9453536f9bbc 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -88,6 +88,7 @@ struct thread_info { #define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */ #define TIF_UPROBE 12 /* breakpointed or singlestepping */ #define TIF_PATCH_PENDING 13 /* pending live patching update */ +#define TIF_NEED_FPU_LOAD 14 /* load FPU on return to userspace */ #define TIF_NOCPUID 15 /* CPUID is not accessible in userland */ #define TIF_NOTSC 16 /* TSC is not accessible in userland */ #define TIF_IA32 17 /* IA32 compatibility process */ @@ -117,6 +118,7 @@ struct thread_info { #define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY) #define _TIF_UPROBE (1 << TIF_UPROBE) #define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING) +#define _TIF_NEED_FPU_LOAD (1 << TIF_NEED_FPU_LOAD) #define _TIF_NOCPUID (1 << TIF_NOCPUID) #define _TIF_NOTSC (1 << TIF_NOTSC) #define _TIF_IA32 (1 << TIF_IA32)
Add TIF_NEED_FPU_LOAD. This is reserved for loading the FPU registers before returning to userland. This flag must not be set for systems without a FPU. If this flag is cleared, the CPU's FPU register hold the current content of current()'s FPU register. The in-memory copy (union fpregs_state) is not valid. If this flag is set, then all of CPU's FPU register may hold a random value (except for PKRU) and it is required to load the content of the FPU register on return to userland. It is introduced now, so we can add code handling it now before adding the main feature. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- arch/x86/include/asm/thread_info.h | 2 ++ 1 file changed, 2 insertions(+)