Commit-ID: 1d731e731c4cd7cbd3b1aa295f0932e7610da82f Gitweb: https://git.kernel.org/tip/1d731e731c4cd7cbd3b1aa295f0932e7610da82f Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> AuthorDate: Wed, 3 Apr 2019 18:41:53 +0200 Committer: Borislav Petkov <bp@xxxxxxx> CommitDate: Fri, 12 Apr 2019 20:04:49 +0200 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: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxx> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: "Jason A. Donenfeld" <Jason@xxxxxxxxx> Cc: kvm ML <kvm@xxxxxxxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Cc: x86-ml <x86@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20190403164156.19645-25-bigeasy@xxxxxxxxxxxxx --- arch/x86/kernel/fpu/signal.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 6df1f15e0cd5..a1bd7be70206 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -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); @@ -327,8 +327,27 @@ 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;
