From: Mark Rutland <mark.rutland@arm.com>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, catalin.marinas@arm.com,
dave.martin@arm.com, hch@infradead.org, james.morse@arm.com,
linux@dominikbrodowski.net, linux-fsdevel@vger.kernel.org,
marc.zyngier@arm.com, viro@zeniv.linux.org.uk
Subject: Re: [PATCHv4 11/19] arm64: don't reload GPRs after apply_ssbd
Date: Mon, 9 Jul 2018 15:21:59 +0100 [thread overview]
Message-ID: <20180709142159.tsxgwhjm3qziymym@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20180706163844.GB27483@arm.com>
On Fri, Jul 06, 2018 at 05:38:45PM +0100, Will Deacon wrote:
> On Mon, Jul 02, 2018 at 12:04:07PM +0100, Mark Rutland wrote:
> > Now that all of the syscall logic works on the saved pt_regs, apply_ssbd
> > can safely corrupt x0-x3 in the entry paths, and we no longer need to
> > restore them. So let's remove the logic doing so.
> >
> > With that logic gone, we can fold the branch target into the macro, so
> > that callers need not deal with this. GAS provides \@, which provides a
> > unique value per macro invocation, which we can use to create a unique
> > label.
> >
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Acked-by: Marc Zyngier <marc.zyngier@arm.com>
> > Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Will Deacon <will.deacon@arm.com>
> > ---
> > arch/arm64/kernel/entry.S | 20 +++++++-------------
> > 1 file changed, 7 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> > index c41b84d06644..728bc7cc5bbb 100644
> > --- a/arch/arm64/kernel/entry.S
> > +++ b/arch/arm64/kernel/entry.S
> > @@ -130,20 +130,21 @@ alternative_else_nop_endif
> >
> > // This macro corrupts x0-x3. It is the caller's duty
> > // to save/restore them if required.
> > - .macro apply_ssbd, state, targ, tmp1, tmp2
> > + .macro apply_ssbd, state, tmp1, tmp2
> > #ifdef CONFIG_ARM64_SSBD
> > alternative_cb arm64_enable_wa2_handling
> > - b \targ
> > + b skip_apply_ssbd\@
> > alternative_cb_end
> > ldr_this_cpu \tmp2, arm64_ssbd_callback_required, \tmp1
> > - cbz \tmp2, \targ
> > + cbz \tmp2, skip_apply_ssbd\@
> > ldr \tmp2, [tsk, #TSK_TI_FLAGS]
> > - tbnz \tmp2, #TIF_SSBD, \targ
> > + tbnz \tmp2, #TIF_SSBD, skip_apply_ssbd\@
>
> Talking to Dave, he makes a good point that this is pretty fragile if a
> macro expansion within the macro itself uses \@, since this would result
> in an unexpected label update and everything would go wrong.
I don't believe that's a problem; \@ is handled as-if it's a named
argument to the macro, and is not incremented within the scope of a
single macro expansion.
e.g. if I assemble:
----
.macro nop_macro
.endm
.macro a n
a_pre_\n\()_\@:
.quad 0
a_post_\n\()_\@:
.quad 0
.endm
.macro b n
b_pre_\n\()_\@:
.quad 0
a \n
b_post_\n\()_\@:
.quad 0
.endm
.macro c n
c_pre_\n\()_\@:
.quad 0
b \n
c_post_\n\()_\@:
.quad 0
.endm
.data
a 0
b 1
c 2
----
... then objdump -D gives me:
----
Disassembly of section .data:
0000000000000000 <a_pre_0_0>:
...
0000000000000008 <a_post_0_0>:
...
0000000000000010 <b_pre_1_1>:
...
0000000000000018 <a_pre_1_2>:
...
0000000000000020 <a_post_1_2>:
...
0000000000000028 <b_post_1_1>:
...
0000000000000030 <c_pre_2_3>:
...
0000000000000038 <b_pre_2_4>:
...
0000000000000040 <a_pre_2_5>:
...
0000000000000048 <a_post_2_5>:
...
0000000000000050 <b_post_2_4>:
...
0000000000000058 <c_post_2_3>:
...
----
... where things are obviously nesting just fine.
Thanks,
Mark.
next prev parent reply other threads:[~2018-07-09 14:22 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-02 11:03 [PATCHv4 00/19] arm64: invoke syscalls with pt_regs Mark Rutland
2018-07-02 11:03 ` [PATCHv4 01/19] arm64: consistently use unsigned long for thread flags Mark Rutland
2018-07-02 11:03 ` [PATCHv4 02/19] arm64: move SCTLR_EL{1,2} assertions to <asm/sysreg.h> Mark Rutland
2018-07-02 11:03 ` [PATCHv4 03/19] arm64: kill config_sctlr_el1() Mark Rutland
2018-07-02 11:04 ` [PATCHv4 04/19] arm64: kill change_cpacr() Mark Rutland
2018-07-02 11:04 ` [PATCHv4 05/19] arm64: move sve_user_{enable,disable} to <asm/fpsimd.h> Mark Rutland
2018-07-02 11:04 ` [PATCHv4 06/19] arm64: remove sigreturn wrappers Mark Rutland
2018-07-02 11:04 ` [PATCHv4 07/19] arm64: convert raw syscall invocation to C Mark Rutland
2018-07-02 11:04 ` [PATCHv4 08/19] arm64: convert syscall trace logic " Mark Rutland
2018-07-02 11:04 ` [PATCHv4 09/19] arm64: convert native/compat syscall entry " Mark Rutland
2018-07-02 11:04 ` [PATCHv4 10/19] arm64: don't restore GPRs when context tracking Mark Rutland
2018-07-02 11:04 ` [PATCHv4 11/19] arm64: don't reload GPRs after apply_ssbd Mark Rutland
2018-07-06 16:38 ` Will Deacon
2018-07-09 14:21 ` Mark Rutland [this message]
2018-07-10 10:37 ` Dave Martin
2018-07-10 17:33 ` Will Deacon
2018-07-11 9:46 ` Mark Rutland
2018-07-02 11:04 ` [PATCHv4 12/19] arm64: zero GPRs upon entry from EL0 Mark Rutland
2018-07-02 11:04 ` [PATCHv4 13/19] kernel: add ksys_personality() Mark Rutland
2018-07-02 11:04 ` [PATCHv4 14/19] kernel: add kcompat_sys_{f,}statfs64() Mark Rutland
2018-07-02 11:04 ` [PATCHv4 15/19] arm64: remove in-kernel call to sys_personality() Mark Rutland
2018-07-02 11:04 ` [PATCHv4 16/19] arm64: use {COMPAT,}SYSCALL_DEFINE0 for sigreturn Mark Rutland
2018-07-02 11:04 ` [PATCHv4 17/19] arm64: use SYSCALL_DEFINE6() for mmap Mark Rutland
2018-07-02 11:04 ` [PATCHv4 18/19] arm64: convert compat wrappers to C Mark Rutland
2018-07-02 11:04 ` [PATCHv4 19/19] arm64: implement syscall wrappers Mark Rutland
2018-07-06 16:42 ` [PATCHv4 00/19] arm64: invoke syscalls with pt_regs Will Deacon
2018-07-10 10:39 ` Will Deacon
2018-07-11 10:47 ` Mark Rutland
2018-07-11 12:27 ` Will Deacon
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180709142159.tsxgwhjm3qziymym@lakrids.cambridge.arm.com \
--to=mark.rutland@arm.com \
--cc=catalin.marinas@arm.com \
--cc=dave.martin@arm.com \
--cc=hch@infradead.org \
--cc=james.morse@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@dominikbrodowski.net \
--cc=marc.zyngier@arm.com \
--cc=viro@zeniv.linux.org.uk \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).