From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: [PATCH 05/24] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Date: Thu, 21 Mar 2019 21:26:13 +0100 Message-ID: <20190321202632.16810-6-bigeasy@linutronix.de> References: <20190321202632.16810-1-bigeasy@linutronix.de> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Cc: x86@kernel.org, Andy Lutomirski , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , kvm@vger.kernel.org, "Jason A. Donenfeld" , Rik van Riel , Dave Hansen , Sebastian Andrzej Siewior To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <20190321202632.16810-1-bigeasy@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org With lazy-FPU support the (now named variable) ->initialized was set to true if the CPU's FPU registers were holding the a valid state of the FPU registers for the active process. If it was set to false then the FPU state was saved in fpu->state and the FPU was deactivated. With lazy-FPU gone, ->initialized is always true for user threads and kernel threads never this function so ->initialized is always true in copy_fpstate_to_sigframe(). The using_compacted_format() check is also a leftover from the lazy-FPU time. In the `->initialized == false' case copy_to_user() would copy the compacted buffer while userland would expect the non-compacted format instead. So in order to save the FPU state in the non-compacted form it issues the xsave opcode to save the *current* FPU state. The FPU is not enabled so the attempt raises the FPU trap, the trap restores the FPU content and re-enables the FPU and the xsave opcode is invoked again and succeeds. *This* does not longer work since commit bef8b6da9522 ("x86/fpu: Handle #NM without FPU emulation as an error") Remove check for ->initialized because it is always true and remove the false condition. Update the comment to reflect that the "state is always live". Signed-off-by: Sebastian Andrzej Siewior --- arch/x86/kernel/fpu/signal.c | 35 ++++++++--------------------------- 1 file changed, 8 insertions(+), 27 deletions(-) diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index a874931edf6a9..de83d0ed9e14e 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -144,9 +144,8 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf) * buf == buf_fx for 64-bit frames and 32-bit fsave frame. * buf != buf_fx for 32-bit frames with fxstate. * - * If the fpu, extended register state is live, save the state directly - * to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise, - * copy the thread's fpu state to the user frame starting at 'buf_fx'. + * Save the state directly to the user frame pointed by the aligned pointer + * 'buf_fx'. * * If this is a 32-bit frame with fxstate, put a fsave header before * the aligned state at 'buf_fx'. @@ -157,7 +156,6 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf) int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size) { struct fpu *fpu = ¤t->thread.fpu; - struct xregs_state *xsave = &fpu->state.xsave; struct task_struct *tsk = current; int ia32_fxstate = (buf != buf_fx); @@ -172,29 +170,12 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size) sizeof(struct user_i387_ia32_struct), NULL, (struct _fpstate_32 __user *) buf) ? -1 : 1; - if (fpu->initialized || using_compacted_format()) { - /* Save the live register state to the user directly. */ - if (copy_fpregs_to_sigframe(buf_fx)) - return -1; - /* Update the thread's fxstate to save the fsave header. */ - if (ia32_fxstate) - copy_fxregs_to_kernel(fpu); - } else { - /* - * It is a *bug* if kernel uses compacted-format for xsave - * area and we copy it out directly to a signal frame. It - * should have been handled above by saving the registers - * directly. - */ - if (boot_cpu_has(X86_FEATURE_XSAVES)) { - WARN_ONCE(1, "x86/fpu: saving compacted-format xsave area to a signal frame!\n"); - return -1; - } - - fpstate_sanitize_xstate(fpu); - if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size)) - return -1; - } + /* Save the live register state to the user directly. */ + if (copy_fpregs_to_sigframe(buf_fx)) + return -1; + /* Update the thread's fxstate to save the fsave header. */ + if (ia32_fxstate) + copy_fxregs_to_kernel(fpu); /* Save the fsave header for the 32-bit frames. */ if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf)) -- 2.20.1