linux-kernel - Re: [PATCH 1/2] xen: make HYPERVISOR_get_debugreg() always

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Date:   Thu, 25 Nov 2021 16:04:11 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Andrew Cooper <amc96@...f.net>, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 1/2] xen: make HYPERVISOR_get_debugreg() always_inline

On 25.11.21 16:00, Andrew Cooper wrote:
> On 25/11/2021 09:20, Juergen Gross wrote:
>> HYPERVISOR_get_debugreg() is being called from noinstr code, so it
>> should be attributed "always_inline".
>>
>> Fixes: f4afb713e5c3a4419ba ("x86/xen: Make get_debugreg() noinstr")
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>   arch/x86/include/asm/xen/hypercall.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
>> index 0575f5863b7f..28ca1119606b 100644
>> --- a/arch/x86/include/asm/xen/hypercall.h
>> +++ b/arch/x86/include/asm/xen/hypercall.h
>> @@ -287,7 +287,7 @@ HYPERVISOR_set_debugreg(int reg, unsigned long value)
>>   	return _hypercall2(int, set_debugreg, reg, value);
>>   }
>>   
>> -static inline unsigned long
>> +static __always_inline unsigned long
>>   HYPERVISOR_get_debugreg(int reg)
>>   {
>>   	return _hypercall1(unsigned long, get_debugreg, reg);
> 
> All this is going to do is push the error one step further in.
> 
> Next, objtool will complain that hypercall_page isn't noinstr.

I don't think so:

.pushsection .noinstr.text, "ax"
         .balign PAGE_SIZE
SYM_CODE_START(hypercall_page)
         .rept (PAGE_SIZE / 32)
                 UNWIND_HINT_FUNC
                 .skip 31, 0x90
                 ret
         .endr


Juergen

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