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b=W1bXm+0oPfT5rDH/gS1gYxYx9XKTMh6rp+TBMPIZ9U+PxxhI8paxDD5MCdN5UQgri FmajXDHHp6E56+SgsXq7hkOtIFxeU/w8oqVN7POD8IIcl3lTmNPUvxGDEyML0wlU1f bSb//6X0qRzGlKMMLF0tOBlVRnDMQyvCNOaZz1EeZMjoalhUMXUURShIo5NpPosK6D Cf4YlXb+WuvmMM1hJzgdD3vtdIS+LSaO2hnr22CIcb+WvZhUb+KtAFJMDbuXhpqRFi 3KWYLNt3r9fLxjZU7NJ3vQXTv0ORLSiGSpf3VapXXxejjX/V4H9157N13si/TqnQgs inaj0ZFsXetKQ== Received: by mail-ej1-f45.google.com with SMTP id a640c23a62f3a-a1915034144so28001566b.0 for ; Thu, 04 Jan 2024 00:58:27 -0800 (PST) X-Gm-Message-State: AOJu0YwSMTjHDi0BzPoJ4RHX+sOh6R8qQNLXeM+3MI8grGc3fLN2HgKk 2b/N3l6RPXI7Sa72+mZesm0ek51PmChS+yb2OW4= X-Google-Smtp-Source: AGHT+IHQVPwm12+OlEILyIKcXqjXe7xvDeITRMmcqOceIIL7hs/JLrObgNNCkATamQIcelA4TEK/rAkJk+QMqBGQsfU= X-Received: by 2002:a17:906:bc45:b0:a28:d45:33ee with SMTP id s5-20020a170906bc4500b00a280d4533eemr152937ejv.143.1704358706430; Thu, 04 Jan 2024 00:58:26 -0800 (PST) MIME-Version: 1.0 References: <20240102123706.6099-2-xry111@xry111.site> In-Reply-To: <20240102123706.6099-2-xry111@xry111.site> From: Huacai Chen Date: Thu, 4 Jan 2024 16:58:21 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3] LoongArch: Fix and simplify fcsr initialization on execve To: Xi Ruoyao Cc: WANG Xuerui , Jiaxun Yang , Eric Biederman , Kees Cook , Tiezhu Yang , Jinyang He , loongarch@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mips@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 8A9A9180004 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: bbo19hn8it1ogtwzx34ku7qrkea51yk3 X-HE-Tag: 1704358710-607139 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Queued for loongarch-next, thanks. Huacai On Tue, Jan 2, 2024 at 8:38=E2=80=AFPM Xi Ruoyao wrote= : > > There has been a lingering bug in LoongArch Linux systems causing some > GCC tests to intermittently fail (see Closes link). I've made a minimal > reproducer: > > zsh% cat measure.s > .align 4 > .globl _start > _start: > movfcsr2gr $a0, $fcsr0 > bstrpick.w $a0, $a0, 16, 16 > beqz $a0, .ok > break 0 > .ok: > li.w $a7, 93 > syscall 0 > zsh% cc mesaure.s -o measure -nostdlib > zsh% echo $((1.0/3)) > 0.33333333333333331 > zsh% while ./measure; do ; done > > This while loop should not stop as POSIX is clear that execve must set > fenv to the default, where FCSR should be zero. But in fact it will > just stop after running for a while (normally less than 30 seconds). > Note that "$((1.0/3))" is needed to reproduce the issue because it > raises FE_INVALID and makes fcsr0 non-zero. > > The problem is we are relying on SET_PERSONALITY2 to reset > current->thread.fpu.fcsr. But SET_PERSONALITY2 is executed before > start_thread which calls lose_fpu(0). We can see if kernel preempt is > enabled, we may switch to another thread after SET_PERSONALITY2 but > before lose_fpu(0). Then bad thing happens: during the thread switch > the value of the fcsr0 register is stored into current->thread.fpu.fcsr, > making it dirty again. > > The issue can be fixed by setting current->thread.fpu.fcsr after > lose_fpu(0) because lose_fpu clears TIF_USEDFPU, then the thread > switch won't touch current->thread.fpu.fcsr. > > The only other architecture setting FCSR in SET_PERSONALITY2 is MIPS. > I've ran a similar test on MIPS with mainline kernel and it turns out > MIPS is buggy too. Anyway MIPS do this for supporting different FP > flavors (NaN encodings etc.) which do not exist on LoongArch. So for > LoongArch, we can simply remove the current->thread.fpu.fcsr setting > from SET_PERSONALITY2 and do it in start_thread, after lose_fpu(0). > I'll leave the job to fix MIPS for MIPS maintainers. > > The while loop failing with the mainline kernel has survived one hour > after this change on LoongArch. > > Closes: https://github.com/loongson-community/discussions/issues/7 > Fixes: 803b0fc5c3f2 ("LoongArch: Add process management") > Link: https://lore.kernel.org/linux-mips/7a6aa1bbdbbe2e63ae96ff163fab0349= f58f1b9e.camel@xry111.site/ > Cc: stable@vger.kernel.org > Cc: linux-mips@vger.kernel.org > Signed-off-by: Xi Ruoyao > --- > > v2 -> v3: > - Update the commit message to mention MIPS is buggy too. > - Replace tabs in the commit message with whitespaces. > - No code change. > > v1 -> v2: > - Still set current->thread.fpu.fcsr to boot_cpu_data.fpu_csr0 instead > of constant 0. > > arch/loongarch/include/asm/elf.h | 5 ----- > arch/loongarch/kernel/elf.c | 5 ----- > arch/loongarch/kernel/process.c | 1 + > 3 files changed, 1 insertion(+), 10 deletions(-) > > diff --git a/arch/loongarch/include/asm/elf.h b/arch/loongarch/include/as= m/elf.h > index 9b16a3b8e706..f16bd42456e4 100644 > --- a/arch/loongarch/include/asm/elf.h > +++ b/arch/loongarch/include/asm/elf.h > @@ -241,8 +241,6 @@ void loongarch_dump_regs64(u64 *uregs, const struct p= t_regs *regs); > do { \ > current->thread.vdso =3D &vdso_info; = \ > \ > - loongarch_set_personality_fcsr(state); \ > - \ > if (personality(current->personality) !=3D PER_LINUX) = \ > set_personality(PER_LINUX); \ > } while (0) > @@ -259,7 +257,6 @@ do { = \ > clear_thread_flag(TIF_32BIT_ADDR); \ > \ > current->thread.vdso =3D &vdso_info; = \ > - loongarch_set_personality_fcsr(state); \ > \ > p =3D personality(current->personality); = \ > if (p !=3D PER_LINUX32 && p !=3D PER_LINUX) = \ > @@ -340,6 +337,4 @@ extern int arch_elf_pt_proc(void *ehdr, void *phdr, s= truct file *elf, > extern int arch_check_elf(void *ehdr, bool has_interpreter, void *interp= _ehdr, > struct arch_elf_state *state); > > -extern void loongarch_set_personality_fcsr(struct arch_elf_state *state)= ; > - > #endif /* _ASM_ELF_H */ > diff --git a/arch/loongarch/kernel/elf.c b/arch/loongarch/kernel/elf.c > index 183e94fc9c69..0fa81ced28dc 100644 > --- a/arch/loongarch/kernel/elf.c > +++ b/arch/loongarch/kernel/elf.c > @@ -23,8 +23,3 @@ int arch_check_elf(void *_ehdr, bool has_interpreter, v= oid *_interp_ehdr, > { > return 0; > } > - > -void loongarch_set_personality_fcsr(struct arch_elf_state *state) > -{ > - current->thread.fpu.fcsr =3D boot_cpu_data.fpu_csr0; > -} > diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/proc= ess.c > index 767d94cce0de..3f9cae615f52 100644 > --- a/arch/loongarch/kernel/process.c > +++ b/arch/loongarch/kernel/process.c > @@ -92,6 +92,7 @@ void start_thread(struct pt_regs *regs, unsigned long p= c, unsigned long sp) > clear_used_math(); > regs->csr_era =3D pc; > regs->regs[3] =3D sp; > + current->thread.fpu.fcsr =3D boot_cpu_data.fpu_csr0; > } > > void flush_thread(void) > -- > 2.43.0 >