From nobody Wed Dec 17 13:55:59 2025 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B37FC1B85D1 for ; Tue, 18 Mar 2025 07:08:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742281714; cv=none; b=q903VGOZPElsaWafkjFZDDZkmtGlfJXMpneiG4JdtP5oqwn/Tf/p72vSpgi9mUaUjEZOHd3BYVxVGGaCGgHp5XKtSX/CnwKktchE02w6pcqPCcdY00ODs3X2yHu/Xf7mT9vqn+MFgyruIAJQ+yTSAfmndrDy73cAzJlsqC2HKlM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742281714; c=relaxed/simple; bh=0cFJ4VVs791QCz3enuVze+W88ph4YL+I2tbcxnQsK5w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=fGzyK/htVt0Ns3MttJZCvMfqIgfRBX9ZaNwKJkl3LRy2FmMZ6ouzW9S1HVt7SZQK8JInEjKkF3WRrcYBOnxfZ9ov0H7TYr3awwar2FtvmRY9wAFP6niDAV9ARobbxfsJFguWEIfD+kUW2TKvfgeaoRT63pNNMeUX/U0pNWSTgbQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=m79JoJwO; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="m79JoJwO" Received: from terminus.zytor.com (terminus.zytor.com [IPv6:2607:7c80:54:3:0:0:0:136]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 52I781go903065 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Tue, 18 Mar 2025 00:08:05 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 52I781go903065 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025021701; t=1742281686; bh=+rraYKRVw/pFe8UExIA58uxW3mfuEYVNH3yjgUiiM/I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=m79JoJwOITt+S1+MdkjkM1rrxTQ/XKyLW010ubRmIxBdw21lUIbT/GhO0E1ybY0Ju Ap10mMA/6yVx9rTjbgbfvWLB9UhOj+3HZj71jmLFoMtwlddRlzUxG5ZF4ecAvvsEtz AnSL8174WaUE2Q9dCiaPZZVn1TkfSrJD5o30S8N/JZlvb0UsEQC7eierL4EHh4J79m gCsSlJPp1ryfm5vAKQyMPAra4mD6UxlQdqipaXyl2t5Fn1zTxYboBTPYk05OqFWyPU WQZzM9iNOKevlvw0jqLOX36tkFUvvCD/Uv0mhiBK6XgyTqpd9fo5DGIiaCfxfiixGi WoO8dUeblKmNw== From: "Xin Li (Intel)" To: linux-kernel@vger.kernel.org Cc: luto@kernel.org, tglx@linutronix.de, mingo@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, brgerst@gmail.com Subject: [PATCH v2 1/3] x86/fred: Allow variable-sized event frame Date: Tue, 18 Mar 2025 00:07:59 -0700 Message-ID: <20250318070801.903045-2-xin@zytor.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250318070801.903045-1-xin@zytor.com> References: <20250318070801.903045-1-xin@zytor.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" A FRED event frame could contain different amount of information for different event types, or perhaps even for different instances of the same event type. Thus the size of an event frame pushed by a FRED CPU is not fixed and the address of the pt_regs structure that is used to save a user level context of current task is not at a fixed offset from top of current task kernel stack. Add a new field named 'user_pt_regs' in the thread_info structure to save the address of user level context pt_regs structure, thus to eliminate the need of any advance information of event frame size and allow a FRED CPU to push variable-sized event frame. For IDT user level event delivery, a pt_regs structure is pushed by hardware and software _always_ at a fixed offset from top of current task kernel stack, so simply initialize user_pt_regs to point to the pt_regs structure no matter whether one is pushed or not. While for FRED user level event delivery, user_pt_regs is updated with a pt_regs structure pointer generated in asm_fred_entrypoint_user(). Suggested-by: H. Peter Anvin (Intel) Signed-off-by: Xin Li (Intel) --- arch/x86/entry/entry_fred.c | 22 ++++++++++++++++++++++ arch/x86/include/asm/processor.h | 18 ++++++++++++------ arch/x86/include/asm/thread_info.h | 9 ++++++--- arch/x86/kernel/process.c | 22 ++++++++++++++++++++++ include/linux/thread_info.h | 1 + kernel/fork.c | 6 ++++++ 6 files changed, 69 insertions(+), 9 deletions(-) diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c index f004a4dc74c2..1d54d451acb6 100644 --- a/arch/x86/entry/entry_fred.c +++ b/arch/x86/entry/entry_fred.c @@ -228,6 +228,28 @@ __visible noinstr void fred_entry_from_user(struct pt_= regs *regs) /* Invalidate orig_ax so that syscall_get_nr() works correctly */ regs->orig_ax =3D -1; =20 + /* + * A FRED event frame could contain different amount of information + * for different event types, or perhaps even for different instances + * of the same event type. Thus the size of an event frame pushed by + * a FRED CPU is not fixed and the address of the pt_regs structure + * that is used to save a user level context of current task is not + * at a fixed offset from top of current task stack. + * + * Save the address of the pt_regs structure passed from and generated + * in the caller function asm_fred_entrypoint_user() in thread_info so + * that task_pt_regs() can be used to access the pt_regs structure + * containing user level context after this point. + * + * What if another event happens before this point? + * + * Actually, another kernel event could happen earlier, even before the + * pt_regs structure for saving user level context is completely saved. + * It is guaranteed that the handler of the new event will NOT access + * the pt_regs structure of the previous user level event. + */ + current->thread_info.user_pt_regs =3D regs; + switch (regs->fred_ss.type) { case EVENT_TYPE_EXTINT: return fred_extint(regs); diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/proces= sor.h index 5d2f7e5aff26..79d8df28cd59 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -646,12 +646,18 @@ static __always_inline void prefetchw(const void *x) =20 #define task_top_of_stack(task) ((unsigned long)(task_pt_regs(task) + 1)) =20 -#define task_pt_regs(task) \ -({ \ - unsigned long __ptr =3D (unsigned long)task_stack_page(task); \ - __ptr +=3D THREAD_SIZE - TOP_OF_KERNEL_STACK_PADDING; \ - ((struct pt_regs *)__ptr) - 1; \ -}) +/* + * task_pt_regs() no longer converts a fixed offset from top of a task + * kernel stack to a pt_regs structure pointer, but rather returns + * whatever in the thread_info.user_pt_regs field, which contains the + * address of a pt_regs structure used to save a user level context of + * current task. + * + * Note, this can't be converted to an inline function as this header + * file defines 'struct thread_struct' which is used in the task_struct + * structure definition. + */ +#define task_pt_regs(task) ((task)->thread_info.user_pt_regs) =20 #ifdef CONFIG_X86_32 #define INIT_THREAD { \ diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thre= ad_info.h index 9282465eea21..4372f171c65f 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -56,6 +56,7 @@ */ #ifndef __ASSEMBLER__ struct task_struct; +struct pt_regs; #include #include =20 @@ -66,11 +67,13 @@ struct thread_info { #ifdef CONFIG_SMP u32 cpu; /* current CPU */ #endif + struct pt_regs *user_pt_regs; }; =20 -#define INIT_THREAD_INFO(tsk) \ -{ \ - .flags =3D 0, \ +#define INIT_THREAD_INFO(tsk) \ +{ \ + .flags =3D 0, \ + .user_pt_regs =3D (struct pt_regs *)TOP_OF_INIT_STACK - 1, \ } =20 #else /* !__ASSEMBLER__ */ diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 91f6ff618852..58c1cd4ca60a 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -108,6 +108,28 @@ int arch_dup_task_struct(struct task_struct *dst, stru= ct task_struct *src) return 0; } =20 +/* + * Initialize thread_info.user_pt_regs for IDT event delivery. + * + * For IDT user level event delivery, a pt_regs structure is pushed by both + * hardware and software and always resides at a fixed offset from top of + * current task kernel stack, thus thread_info.user_pt_regs is a per-task + * constant and NEVER changes after initialization. + * + * While for FRED user level event delivery, user_pt_regs is updated in + * fred_entry_from_user() immediately after user level event delivery. + * + * Note: thread_info.user_pt_regs of the init task is initialized at build + * time. + */ +void arch_init_user_pt_regs(struct task_struct *tsk) +{ + unsigned long top_of_stack =3D (unsigned long)task_stack_page(tsk) + THRE= AD_SIZE; + + top_of_stack -=3D TOP_OF_KERNEL_STACK_PADDING; + tsk->thread_info.user_pt_regs =3D (struct pt_regs *)top_of_stack - 1; +} + #ifdef CONFIG_X86_64 void arch_release_task_struct(struct task_struct *tsk) { diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index cf2446c9c30d..324667e0b8dd 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -273,6 +273,7 @@ void arch_task_cache_init(void); /* for CONFIG_SH */ void arch_release_task_struct(struct task_struct *tsk); int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src); +void arch_init_user_pt_regs(struct task_struct *tsk); =20 #endif /* __KERNEL__ */ =20 diff --git a/kernel/fork.c b/kernel/fork.c index 8695c345ca49..21af95645d84 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1105,6 +1105,10 @@ int __weak arch_dup_task_struct(struct task_struct *= dst, return 0; } =20 +void __weak arch_init_user_pt_regs(struct task_struct *tsk) +{ +} + void set_task_stack_end_magic(struct task_struct *tsk) { unsigned long *stackend; @@ -1132,6 +1136,8 @@ static struct task_struct *dup_task_struct(struct tas= k_struct *orig, int node) if (err) goto free_tsk; =20 + arch_init_user_pt_regs(tsk); + #ifdef CONFIG_THREAD_INFO_IN_TASK refcount_set(&tsk->stack_refcount, 1); #endif --=20 2.48.1