linux-kernel - Re: [PATCH V8 40/44] memremap_pages: Add pgmap_protection_flag

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Date:   Tue, 1 Mar 2022 18:01:04 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "hpa@...or.com" <hpa@...or.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V8 40/44] memremap_pages: Add
 pgmap_protection_flag_invalid()

On Mon, Jan 31, 2022 at 05:37:17PM -0800, Edgecombe, Rick P wrote:
> On Thu, 2022-01-27 at 09:55 -0800, ira.weiny@...el.com wrote:
> > +/*
> > + * pgmap_protection_flag_invalid - Check and flag an invalid use of
> > a pgmap
> > + *                                 protected page
> > + *
> > + * There are code paths which are known to not be compatible with
> > pgmap
> > + * protections.
> 
> This could get hopefully get stale. Maybe the comment should just
> describe what the function does and leave this reasoning to the commit
> log?

Thanks for the review but based on the thread with Dan this patch is dropped.

Thanks,
Ira

> 
> > pgmap_protection_flag_invalid() is provided as a 'relief
> > + * valve' to be used in those functions which are known to be
> > incompatible.
> > + *
> > + * Thus an invalid use case can be flaged with more precise data
> > rather than
> > + * just flagging a fault.  Like the fault handler code this abandons
> 
> In the commit log you called this "the invalid access on fault" and it
> seemed a little clearer to me then "just flagging a fault".
> 
> > the use of
> > + * the PKS key and optionally allows the calling code path to
> > continue based on
> > + * the configuration of the memremap.pks_fault_mode command line
> > + * (and/or sysfs) option.
> 
> It lets the calling code continue regardless right? It just warns if
> !PKS_MODE_STRICT. Why not warn in the case of PKS_MODE_STRICT too?
> 
> Seems surprising that the stricter setting would have less checks.
> 
> > + */
> > +static inline void pgmap_protection_flag_invalid(struct page *page)
> > +{
> > +       if (!pgmap_check_pgmap_prot(page))
> > +               return;
> > +       __pgmap_protection_flag_invalid(page->pgmap);
> > +}