Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Mime-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset=UTF-8
Date:   Tue, 06 Jun 2023 18:58:46 +1000
Message-Id: <CT5FZBY14ZM4.OYXBJNXQU9A2@wheely>
Cc:     <linux-kernel@vger.kernel.org>, <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH] powerpc/signal32: Force inlining of
 __unsafe_save_user_regs() and save_tm_user_regs_unsafe()
From:   "Nicholas Piggin" <npiggin@gmail.com>
To:     "Christophe Leroy" <christophe.leroy@csgroup.eu>,
        "Michael Ellerman" <mpe@ellerman.id.au>
References: <7e469c8f01860a69c1ada3ca6a5e2aa65f0f74b2.1685955220.git.christophe.leroy@csgroup.eu>
In-Reply-To: <7e469c8f01860a69c1ada3ca6a5e2aa65f0f74b2.1685955220.git.christophe.leroy@csgroup.eu>
Precedence: bulk

On Mon Jun 5, 2023 at 6:58 PM AEST, Christophe Leroy wrote:
> Looking at generated code for handle_signal32() shows calls to a
> function called __unsafe_save_user_regs.constprop.0 while user access
> is open.
>
> And that __unsafe_save_user_regs.constprop.0 function has two nops at
> the begining, allowing it to be traced, which is unexpected during
> user access open window.
>
> The solution could be to mark __unsafe_save_user_regs() no trace, but
> to be on the safe side the most efficient is to flag it __always_inline
> as already done for function __unsafe_restore_general_regs(). The
> function is relatively small and only called twice, so the size
> increase will remain in the noise.
>
> Do the same with save_tm_user_regs_unsafe() as it may suffer the
> same issue.

Could you put a comment so someone doesn't uninline it later? Marking
it notrace as well would be sufficient for a comment, if that works.

Thanks,
Nick

>
> Fixes: ef75e7318294 ("powerpc/signal32: Transform save_user_regs() and sa=
ve_tm_user_regs() in 'unsafe' version")
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/kernel/signal_32.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal=
_32.c
> index c114c7f25645..7a718ed32b27 100644
> --- a/arch/powerpc/kernel/signal_32.c
> +++ b/arch/powerpc/kernel/signal_32.c
> @@ -264,8 +264,9 @@ static void prepare_save_user_regs(int ctx_has_vsx_re=
gion)
>  #endif
>  }
> =20
> -static int __unsafe_save_user_regs(struct pt_regs *regs, struct mcontext=
 __user *frame,
> -				   struct mcontext __user *tm_frame, int ctx_has_vsx_region)
> +static __always_inline int
> +__unsafe_save_user_regs(struct pt_regs *regs, struct mcontext __user *fr=
ame,
> +			struct mcontext __user *tm_frame, int ctx_has_vsx_region)
>  {
>  	unsigned long msr =3D regs->msr;
> =20
> @@ -364,8 +365,9 @@ static void prepare_save_tm_user_regs(void)
>  		current->thread.ckvrsave =3D mfspr(SPRN_VRSAVE);
>  }
> =20
> -static int save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontex=
t __user *frame,
> -				    struct mcontext __user *tm_frame, unsigned long msr)
> +static __always_inline int
> +save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontext __user *f=
rame,
> +			 struct mcontext __user *tm_frame, unsigned long msr)
>  {
>  	/* Save both sets of general registers */
>  	unsafe_save_general_regs(&current->thread.ckpt_regs, frame, failed);
> @@ -444,8 +446,9 @@ static int save_tm_user_regs_unsafe(struct pt_regs *r=
egs, struct mcontext __user
>  #else
>  static void prepare_save_tm_user_regs(void) { }
> =20
> -static int save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontex=
t __user *frame,
> -				    struct mcontext __user *tm_frame, unsigned long msr)
> +static __always_inline int
> +save_tm_user_regs_unsafe(struct pt_regs *regs, struct mcontext __user *f=
rame,
> +			 struct mcontext __user *tm_frame, unsigned long msr)
>  {
>  	return 0;
>  }
> --=20
> 2.40.1