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From: "Andy Lutomirski" <luto@kernel.org>
To: "Ali Raza" <aliraza@bu.edu>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Cc: "Jonathan Corbet" <corbet@lwn.net>,
	masahiroy@kernel.org, michal.lkml@markovi.net,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Arnd Bergmann" <arnd@arndb.de>,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	dietmar.eggemann@arm.com, "Steven Rostedt" <rostedt@goodmis.org>,
	"Ben Segall" <bsegall@google.com>,
	mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	jpoimboe@kernel.org, linux-doc@vger.kernel.org,
	linux-kbuild@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org,
	"the arch/x86 maintainers" <x86@kernel.org>,
	rjones@redhat.com, munsoner@bu.edu, tommyu@bu.edu,
	drepper@redhat.com, lwoodman@redhat.com, mboydmcse@gmail.com,
	okrieg@bu.edu, rmancuso@bu.edu
Subject: Re: [RFC UKL 07/10] x86/signal: Adjust signal handler register values and return frame
Date: Tue, 04 Oct 2022 10:34:12 -0700	[thread overview]
Message-ID: <40484dc2-8da3-486d-9c53-02ae23a50fbb@app.fastmail.com> (raw)
In-Reply-To: <20221003222133.20948-8-aliraza@bu.edu>



On Mon, Oct 3, 2022, at 3:21 PM, Ali Raza wrote:
> For a UKL thread, returning to a signal handler is not done with iret or
> sysret.  This means we need to adjust the way the return stack frame is
> handled for these threads.  When constructing the signal frame, we leave
> the previous frame in place because we will return to it from the signal
> handler.  We also leave space for pushing eflags and the return address.
> UKL threads will only use the __KERNEL_DS value in the ss register and 0xC3
> in the cs register.

This is unclear.  Are you taking about returning from the kernel fault code *to* the signal handler or are you talking about returning *from* the user signal hander to the user code that was running when the signal happened?

In any case, I don't see what this has to do with iret or sysret.  Surely UKL can use a sigreturn() just like regular Linux.

The part where a UKL thread has permission to return to a CPL0 context should be a separate patch.

--Andy

  reply	other threads:[~2022-10-04 17:36 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-03 22:21 [RFC UKL 00/10] Unikernel Linux (UKL) Ali Raza
2022-10-03 22:21 ` [RFC UKL 01/10] kbuild: Add sections and symbols to linker script for UKL support Ali Raza
2022-10-03 22:21 ` [RFC UKL 02/10] x86/boot: Load the PT_TLS segment for Unikernel configs Ali Raza
2022-10-04 17:30   ` Andy Lutomirski
2022-10-06 21:00     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 03/10] sched: Add task_struct tracking of kernel or application execution Ali Raza
2022-10-03 22:21 ` [RFC UKL 04/10] x86/entry: Create alternate entry path for system calls Ali Raza
2022-10-04 17:43   ` Andy Lutomirski
2022-10-06 21:12     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 05/10] x86/uaccess: Make access_ok UKL aware Ali Raza
2022-10-04 17:36   ` Andy Lutomirski
2022-10-06 21:16     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 06/10] x86/fault: Skip checking kernel mode access to user address space for UKL Ali Raza
2022-10-03 22:21 ` [RFC UKL 07/10] x86/signal: Adjust signal handler register values and return frame Ali Raza
2022-10-04 17:34   ` Andy Lutomirski [this message]
2022-10-06 21:20     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 08/10] exec: Make exec path for starting UKL application Ali Raza
2022-10-03 22:21 ` [RFC UKL 09/10] exec: Give userspace a method for starting UKL process Ali Raza
2022-10-04 17:35   ` Andy Lutomirski
2022-10-06 21:25     ` Ali Raza
2022-10-03 22:21 ` [RFC UKL 10/10] Kconfig: Add config option for enabling and sample for testing UKL Ali Raza
2022-10-04  2:11   ` Bagas Sanjaya
2022-10-06 21:28     ` Ali Raza
2022-10-07 10:21       ` Masahiro Yamada
2022-10-13 17:08         ` Ali Raza
2022-10-06 21:27 ` [RFC UKL 00/10] Unikernel Linux (UKL) H. Peter Anvin

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