linux-kernel - Re: [PATCH v5 1/7] mce: fix set_mce_nospec to always unmap the whole page

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Date:   Wed, 2 Feb 2022 21:20:36 +0000
From:   Jane Chu <jane.chu@...cle.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "david@...morbit.com" <david@...morbit.com>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "agk@...hat.com" <agk@...hat.com>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "vgoyal@...hat.com" <vgoyal@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>
Subject: Re: [PATCH v5 1/7] mce: fix set_mce_nospec to always unmap the whole
 page

On 2/2/2022 5:21 AM, Christoph Hellwig wrote:
>> +static inline int set_mce_nospec(unsigned long pfn)
>>   {
>>   	unsigned long decoy_addr;
>>   	int rc;
>> @@ -117,10 +113,7 @@ static inline int set_mce_nospec(unsigned long pfn, bool unmap)
>>   	 */
>>   	decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63));
>>   
>> -	if (unmap)
>> -		rc = set_memory_np(decoy_addr, 1);
>> -	else
>> -		rc = set_memory_uc(decoy_addr, 1);
>> +	rc = set_memory_np(decoy_addr, 1);
>>   	if (rc)
>>   		pr_warn("Could not invalidate pfn=0x%lx from 1:1 map\n", pfn);
>>   	return rc;
>> @@ -130,7 +123,7 @@ static inline int set_mce_nospec(unsigned long pfn, bool unmap)
>>   /* Restore full speculative operation to the pfn. */
>>   static inline int clear_mce_nospec(unsigned long pfn)
>>   {
>> -	return set_memory_wb((unsigned long) pfn_to_kaddr(pfn), 1);
>> +	return _set_memory_present((unsigned long) pfn_to_kaddr(pfn), 1);
>>   }
> 
> Wouldn't it make more sense to move these helpers out of line rather
> than exporting _set_memory_present?

Do you mean to move
   return change_page_attr_set(&addr, numpages, __pgprot(_PAGE_PRESENT), 0);
into clear_mce_nospec() for the x86 arch and get rid of _set_memory_present?
If so, sure I'll do that.

> 
>>   /*
>> - * _set_memory_prot is an internal helper for callers that have been passed
>> + * __set_memory_prot is an internal helper for callers that have been passed
> 
> This looks unrelated to the patch.

My bad, will remove the remnant.

thanks!
-jane