From: Lai Jiangshan <jiangshanlai@gmail.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Jürgen Gross" <jgross@suse.com>,
LKML <linux-kernel@vger.kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Josh Poimboeuf" <jpoimboe@redhat.com>,
"Andy Lutomirski" <luto@kernel.org>,
"Thomas Gleixner" <tglx@linutronix.de>, "X86 ML" <x86@kernel.org>,
"Lai Jiangshan" <jiangshan.ljs@antgroup.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH V6 6/8] x86/entry: Convert SWAPGS to swapgs and remove the definition of SWAPGS
Date: Fri, 29 Apr 2022 19:45:43 +0800 [thread overview]
Message-ID: <CAJhGHyBHPDD=hD-78rQDCj2VfQT21m8JzD-m9DazsUa8VpBVcQ@mail.gmail.com> (raw)
In-Reply-To: <Ymu2XC7k8Xj/vMjG@zn.tnic>
On Fri, Apr 29, 2022 at 5:56 PM Borislav Petkov <bp@alien8.de> wrote:
>
> On Thu, Apr 21, 2022 at 10:10:53PM +0800, Lai Jiangshan wrote:
> > diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> > index 4fdb007cddbd..c5aeb0819707 100644
> > --- a/arch/x86/entry/entry_64_compat.S
> > +++ b/arch/x86/entry/entry_64_compat.S
> > @@ -50,7 +50,7 @@ SYM_CODE_START(entry_SYSENTER_compat)
> > UNWIND_HINT_EMPTY
> > ENDBR
> > /* Interrupts are off on entry. */
> > - SWAPGS
> > + swapgs
> >
> > pushq %rax
> > SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
>
> I'm not sure about this: why can't XENPV do a 32-bit syscall through the vdso?
>
> Also, looking at this, Jürgen, it looks kinda spaghetti to me:
>
> entry_SYSENTER_compat
>
> ...
>
> /* XEN PV guests always use IRET path */
> ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
> "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
>
>
> then at that swapgs_restore_regs_and_return_to_usermode label:
>
> #ifdef CONFIG_XEN_PV
> ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
> #endif
>
>
> Can we simply jump directly to xenpv_restore_regs_and_return_to_usermode
> from entry_SYSENTER_compat or is that CONFIG_DEBUG_ENTRY chunk there
> needed?
Hello
Adding ALTERNATIVE in swapgs_restore_regs_and_return_to_usermode()
results a simpler patch which is better served as a bug fix:
https://lore.kernel.org/lkml/163861832551.11128.1645285137833652414.tip-bot2@tip-bot2/
which is also your suggestion:
https://lore.kernel.org/lkml/YYD9ohN2Zcy4EdMb@zn.tnic/
While the original patch has sprinkled all those ALTERNATIVE calls
everywhere:
https://lore.kernel.org/lkml/20211026141420.17138-5-jiangshanlai@gmail.com/
And this original version has a SYM_L_WEAK placeholder
which is objected to by some people.
Thanks
Lai
next prev parent reply other threads:[~2022-04-29 11:46 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-21 14:10 [PATCH V6 0/8] x86/entry: Clean up entry code Lai Jiangshan
2022-04-21 14:10 ` [PATCH V6 1/8] x86/traps: Move pt_regs only in fixup_bad_iret() Lai Jiangshan
2022-04-21 14:10 ` [PATCH V6 2/8] x86/entry: Switch the stack after error_entry() returns Lai Jiangshan
2022-04-21 14:10 ` [PATCH V6 3/8] x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry() Lai Jiangshan
2022-04-27 17:45 ` Borislav Petkov
2022-04-28 0:33 ` Lai Jiangshan
2022-04-28 10:26 ` Borislav Petkov
2022-05-02 12:42 ` Juergen Gross
2022-05-02 18:09 ` Borislav Petkov
2022-04-21 14:10 ` [PATCH V6 4/8] x86/entry: Move cld to the start of idtentry macro Lai Jiangshan
2022-04-21 14:10 ` [PATCH V6 5/8] x86/entry: Don't call error_entry() for XENPV Lai Jiangshan
2022-04-21 14:10 ` [PATCH V6 6/8] x86/entry: Convert SWAPGS to swapgs and remove the definition of SWAPGS Lai Jiangshan
2022-04-29 9:56 ` Borislav Petkov
2022-04-29 11:45 ` Lai Jiangshan [this message]
2022-04-29 12:22 ` Borislav Petkov
2022-05-02 12:18 ` Juergen Gross
2022-05-02 17:56 ` Borislav Petkov
2022-05-03 10:43 ` Borislav Petkov
2022-04-21 14:10 ` [PATCH V6 7/8] x86/entry: Remove the branch in sync_regs() Lai Jiangshan
2022-04-21 14:10 ` [PATCH V6 8/8] x86/entry: Use idtentry macro for entry_INT80_compat() Lai Jiangshan
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