From mboxrd@z Thu Jan 1 00:00:00 1970 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 5BB94E552 for ; Wed, 19 Mar 2025 06:48:06 +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=1742366889; cv=none; b=kq00lbLrI1DKMgFtro9jhsXW/BMAopUrhkQj68Bwq3oJ/Rvh80DFP+WWofN2J4lJJMtCeuKaP8A9VMIG7MPgbFwYEi0DIpkvt/w4hDNs+60Mx1L1lR8+YlK/JaQz9N0aUTQSlqEYC+ggRthgdEGw0Rw6WYb2KBnbRLDRFQC6iO0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742366889; c=relaxed/simple; bh=ZL9d0TPFiTuCK3GMVeoEzec8w54xMz19V7ROiHnIS8g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Q9YOs2MULwLHYF9rZU1XfsFXxcYpzWEiLOqLgFxKIcOAr5WSyfpfqHHc0BKAu1DzH38VfwwY7Y8R/BkKy7FUnk14xneZqgwV59ORbbxwKLeXq2CpY6Jwyo5auHwv0xrgadqICN8kRc1gpyW4mVTa+79DLvrQNcHsTkrJtNW+Ung= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FByVMV3pdSyajg9aJSD/yLU1CEufI65K2naHAMBpvudWItEUS6Jjywjs3eKTfn1gP wyl0yWZf6pj2FYQitwJbikOpJCEVp/bSCKJVk755y1OVMVnMvVLUXUjRfDsXlQ7V54 Xcq2oec96VJNmUHL+fscZu/xETwNr4c21IzPmsVZ4iZF75rcFhGnnfmnHfmDEmttPr m6oGsiqASIE3Nclog1vDsnjVhxF4CN/z/Y5qahnljRXS6Z+2meL/7OaYdtX4XaTNci OmR6OcZHTw9mk6qoD8xoVZsksN0lIpw2Z6744t+vNlQvUn2ih0x85MfZsAHWmAupxI oy1ms0gfV9/2g== Message-ID: <7b0484d2-3608-4243-b3ae-2b49e2a32331@zytor.com> Date: Tue, 18 Mar 2025 23:47:32 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RESEND PATCH v2 1/3] x86/fred: Allow variable-sized event frame To: Brian Gerst Cc: linux-kernel@vger.kernel.org, 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 References: <20250318071947.907364-1-xin@zytor.com> <20250318071947.907364-2-xin@zytor.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/18/2025 6:53 AM, Brian Gerst wrote: >> -#define INIT_THREAD_INFO(tsk) \ >> -{ \ >> - .flags = 0, \ >> +#define INIT_THREAD_INFO(tsk) \ >> +{ \ >> + .flags = 0, \ >> + .user_pt_regs = (struct pt_regs *)TOP_OF_INIT_STACK - 1, \ > > Use __top_init_kernel_stack here. Will do. > >> } >> >> #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, struct task_struct *src) >> return 0; >> } >> >> +/* >> + * 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 = (unsigned long)task_stack_page(tsk) + THREAD_SIZE; >> + >> + top_of_stack -= TOP_OF_KERNEL_STACK_PADDING; >> + tsk->thread_info.user_pt_regs = (struct pt_regs *)top_of_stack - 1; >> +} > > Can this be put into arch_dup_task_struct() instead of creating another hook? I wanted to do it at the beginning but task stack is no longer part of the task_struct on x86. Make sense? Thanks! Xin