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 23:07:37 +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 1:20 PM, Jane Chu wrote:
> 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.

Looks like I can't do that.  It's either exporting 
_set_memory_present(), or exporting change_page_attr_set().  Perhaps the 
former is more conventional?

-jane