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[221.241.217.81]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3159df71ea8sm4210760a91.7.2025.06.21.05.40.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 21 Jun 2025 05:40:27 -0700 (PDT) Date: Sat, 21 Jun 2025 21:40:24 +0900 Message-ID: From: Hajime Tazaki To: benjamin@sipsolutions.net Cc: linux-um@lists.infradead.org, ricarkol@google.com, Liam.Howlett@oracle.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 04/13] x86/um: nommu: syscall handling In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/26.3 Mule/6.0 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=ISO-2022-JP X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250621_054029_903024_BB1B2FDF X-CRM114-Status: GOOD ( 20.22 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On Thu, 19 Jun 2025 19:31:53 +0900, Benjamin Berg wrote: > > diff --git a/arch/x86/um/nommu/do_syscall_64.c b/arch/x86/um/nommu/do_syscall_64.c > > new file mode 100644 > > index 000000000000..5d0fa83e7fdc > > --- /dev/null > > +++ b/arch/x86/um/nommu/do_syscall_64.c > > @@ -0,0 +1,37 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +__visible void do_syscall_64(struct pt_regs *regs) > > +{ > > + int syscall; > > + > > + syscall = PT_SYSCALL_NR(regs->regs.gp); > > + UPT_SYSCALL_NR(®s->regs) = syscall; > > + > > + pr_debug("syscall(%d) (current=%lx) (fn=%lx)\n", > > + syscall, (unsigned long)current, > > + (unsigned long)sys_call_table[syscall]); > > You probably want to drop the pr_debug from the syscall path. okay, I'll update those parts. > > + if (likely(syscall < NR_syscalls)) { > > + PT_REGS_SET_SYSCALL_RETURN(regs, > > + EXECUTE_SYSCALL(syscall, regs)); > > + } > > + > > + pr_debug("syscall(%d) --> %lx\n", syscall, > > + regs->regs.gp[HOST_AX]); > > + > > + PT_REGS_SYSCALL_RET(regs) = regs->regs.gp[HOST_AX]; > > + > > + /* execve succeeded */ > > + if (syscall == __NR_execve && regs->regs.gp[HOST_AX] == 0) > > + userspace(¤t->thread.regs.regs); > > That said, this is what I am stumbling over. Why do you need to jump > into userspace() here? It seems odd to me to need a special case in the > syscall path itself. > Aren't there other possibilities to hook/override the kernel task > state? thanks, I found that this is a leftover of our early implementation which doesn't have a proper schedule upon an exit from syscall. we can remove this part and I'll fix them after more investigation. > > + /* force do_signal() --> is_syscall() */ > > + set_thread_flag(TIF_SIGPENDING); > > + interrupt_end(); > > Same here. The MMU UML code seems to also do this, but restricted to > ptrace'd processes? Maybe I am just missing something obvious … nommu doesn't have separate process/context to indicate a schedule to the context here (syscall). without that part we do not have a chance to schedule tasks and signals to userspace. But the force on SIGPENDING flag is not actually needed so, I'll remove that part. thanks for pointing out. -- Hajime