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Commit 1d731e73 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Borislav Petkov
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x86/fpu: Add a fastpath to __fpu__restore_sig() 



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: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarDave Hansen <dave.hansen@intel.com>
Reviewed-by: default avatarThomas 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
parent 5f409e20

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;