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Subject: Re: [PATCH] xen/pv: Fix a boot up hang triggered by int3 self test
To:     linux-kernel@vger.kernel.org
Cc:     xen-devel@lists.xenproject.org, x86@kernel.org,
        srinivas.eeda@oracle.com,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
References: <1562820438-30328-1-git-send-email-zhenzhong.duan@oracle.com>
From:   Zhenzhong Duan <zhenzhong.duan@oracle.com>
Organization: Oracle Corporation
Message-ID: <fa73ab45-235d-b338-ddd1-1628ed70d801@oracle.com>
Date:   Fri, 12 Jul 2019 15:41:17 +0800
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Sorry for the noise, it looks description is wrong.

This is not a double pop, but xen pv taking the path

with create_gap=0, I'll send a v2.

Zhenzhong

On 2019/7/11 12:47, Zhenzhong Duan wrote:
> Commit 7457c0da024b ("x86/alternatives: Add int3_emulate_call()
> selftest") reveals a bug in XEN PV int3 assemble code. There is
> a double pop of register R11 and RCX currupting the exception
> frame, one in xen_int3 and the other in xen_xenint3.
>
> We see below hang at bootup:
>
> general protection fault: 0000 [#1] SMP NOPTI
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0+ #6
> RIP: e030:int3_magic+0x0/0x7
> Call Trace:
>   alternative_instructions+0x3d/0x12e
>   check_bugs+0x7c9/0x887
>   ?__get_locked_pte+0x178/0x1f0
>   start_kernel+0x4ff/0x535
>   ?set_init_arg+0x55/0x55
>   xen_start_kernel+0x571/0x57a
>
> Fix it by removing xen_xenint3.
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> ---
>   arch/x86/include/asm/traps.h | 2 +-
>   arch/x86/xen/enlighten_pv.c  | 2 +-
>   arch/x86/xen/xen-asm_64.S    | 1 -
>   3 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
> index 7d6f3f3..f2bd284 100644
> --- a/arch/x86/include/asm/traps.h
> +++ b/arch/x86/include/asm/traps.h
> @@ -40,7 +40,7 @@
>   asmlinkage void xen_divide_error(void);
>   asmlinkage void xen_xennmi(void);
>   asmlinkage void xen_xendebug(void);
> -asmlinkage void xen_xenint3(void);
> +asmlinkage void xen_int3(void);
>   asmlinkage void xen_overflow(void);
>   asmlinkage void xen_bounds(void);
>   asmlinkage void xen_invalid_op(void);
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 4722ba2..2138d69 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -596,7 +596,7 @@ struct trap_array_entry {
>   
>   static struct trap_array_entry trap_array[] = {
>   	{ debug,                       xen_xendebug,                    true },
> -	{ int3,                        xen_xenint3,                     true },
> +	{ int3,                        xen_int3,                        true },
>   	{ double_fault,                xen_double_fault,                true },
>   #ifdef CONFIG_X86_MCE
>   	{ machine_check,               xen_machine_check,               true },
> diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
> index 1e9ef0b..ebf610b 100644
> --- a/arch/x86/xen/xen-asm_64.S
> +++ b/arch/x86/xen/xen-asm_64.S
> @@ -32,7 +32,6 @@ xen_pv_trap divide_error
>   xen_pv_trap debug
>   xen_pv_trap xendebug
>   xen_pv_trap int3
> -xen_pv_trap xenint3
>   xen_pv_trap xennmi
>   xen_pv_trap overflow
>   xen_pv_trap bounds