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Subject: Re: [PATCH 2/2 v2] kdump,vmcoreinfo: Export the value of sme mask to
 vmcoreinfo
To:     Dave Young <dyoung@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        akpm@linux-foundation.org, bhe@redhat.com
References: <20181202030839.29945-1-lijiang@redhat.com>
 <20181202030839.29945-3-lijiang@redhat.com>
 <20181205102407.GB6940@dhcp-128-65.nay.redhat.com>
From:   lijiang <lijiang@redhat.com>
Message-ID: <685758a5-9d52-9270-e907-b4bda49a0102@redhat.com>
Date:   Mon, 10 Dec 2018 11:13:35 +0800
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在 2018年12月05日 18:24, Dave Young 写道:
> On 12/02/18 at 11:08am, Lianbo Jiang wrote:
>> For AMD machine with SME feature, makedumpfile tools need to know
>> whether the crash kernel was encrypted or not. If SME is enabled
>> in the first kernel, the crash kernel's page table(pgd/pud/pmd/pte)
>> contains the memory encryption mask, so need to remove the sme mask
>> to obtain the true physical address.
>>
>> Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
>> ---
>>  arch/x86/kernel/machine_kexec_64.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
>> index 4c8acdfdc5a7..1860fe24117d 100644
>> --- a/arch/x86/kernel/machine_kexec_64.c
>> +++ b/arch/x86/kernel/machine_kexec_64.c
>> @@ -352,10 +352,24 @@ void machine_kexec(struct kimage *image)
>>  
>>  void arch_crash_save_vmcoreinfo(void)
>>  {
>> +	u64 sme_mask = sme_me_mask;
>> +
>>  	VMCOREINFO_NUMBER(phys_base);
>>  	VMCOREINFO_SYMBOL(init_top_pgt);
>>  	vmcoreinfo_append_str("NUMBER(pgtable_l5_enabled)=%d\n",
>>  			pgtable_l5_enabled());
>> +	/*
>> +	 * Currently, the local variable 'sme_mask' stores the value of
>> +	 * sme_me_mask(bit 47), and also write the value of sme_mask to
>> +	 * the vmcoreinfo.
>> +	 * If need, the bit(sme_mask) might be redefined in the future,
>> +	 * but the 'bit63' will be reserved.
>> +	 * For example:
>> +	 * [ misc	   ][ enc bit  ][ other misc SME info       ]
>> +	 * 0000_0000_0000_0000_1000_0000_0000_0000_0000_0000_..._0000
>> +	 * 63   59   55   51   47   43   39   35   31   27   ... 3
>> +	 */
>> +	VMCOREINFO_NUMBER(sme_mask);
> 
> #define VMCOREINFO_NUMBER(name) \
>         vmcoreinfo_append_str("NUMBER(%s)=%ld\n", #name, (long)name)
> 
> VMCOREINFO_NUMBER is defined as above, so it looks questionable to add
> more users of that for different data types although it may work in real
> world.
> 

Thank you, Dave.
For the sme_mask, the bit47 is set '1', and the VMCOREINFO_NUMBER is a signed
64 bit number(x86_64), it is big enough to the sme_mask.


> A new macro like below may be better, may need to choose a better name
> though:
> _VMCOREINFO_NUMBER(name, format, type)
> so you can pass the format specifier and data types explictly
> 

That should be a good suggestion. But for now, maybe it is not time for improving it.
Because it is still big enough.

Thanks.
Lianbo

> 
>>  
>>  #ifdef CONFIG_NUMA
>>  	VMCOREINFO_SYMBOL(node_data);
>> -- 
>> 2.17.1
>>
> 
> Thanks
> Dave
>