x86/fpu: Add a fastpath to __fpu__restore_sig() (1d731e73) · Commits · 戴 / test

The previous commits refactor the restoration of the FPU registers so that they can be loaded from in-kernel memory. This overhead can be avoided if the load can be performed without a pagefault. Attempt to restore FPU registers by invoking copy_user_to_fpregs_zeroing(). If it fails try the slowpath which can handle pagefaults. [ bp: Add a comment over the fastpath to be able to find one's way around the function. ] Signed-off-by:

Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by:

Borislav Petkov <bp@suse.de> Reviewed-by:

Dave Hansen <dave.hansen@intel.com> Reviewed-by:

Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com> Cc: kvm ML <kvm@vger.kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: x86-ml <x86@kernel.org> Link: https://lkml.kernel.org/r/20190403164156.19645-25-bigeasy@linutronix.de

arch/x86/kernel/fpu/signal.c

+21 −2

Original line number	Diff line number	Diff line
		@@ -242,10 +242,10 @@ sanitize_restored_xstate(union fpregs_state *state,
		/*
		* Restore the extended state if present. Otherwise, restore the FP/SSE state.
		*/
		static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
		static int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
		{
		if (use_xsave()) {
		if ((unsigned long)buf % 64 \|\| fx_only) {
		if (fx_only) {
		u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
		copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
		return copy_user_to_fxregs(buf);
		@@ -327,7 +327,26 @@ static int __fpu__restore_sig(void __user buf, void __user buf_fx, int size)
		if (ret)
		goto err_out;
		envp = &env;
		} else {
		/*
		* Attempt to restore the FPU registers directly from user
		* memory. For that to succeed, the user access cannot cause
		* page faults. If it does, fall back to the slow path below,
		* going through the kernel buffer with the enabled pagefault
		* handler.
		*/
		fpregs_lock();
		pagefault_disable();
		ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only);
		pagefault_enable();
		if (!ret) {
		fpregs_mark_activate();
		fpregs_unlock();
		return 0;
		}
		fpregs_unlock();
		}


		if (use_xsave() && !fx_only) {
		u64 init_bv = xfeatures_mask & ~xfeatures;

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