x86/mm/mtrr: Remove kernel internal MTRR interfaces: unexport mtrr_add() and mtrr_del()
The effort to replace mtrr_add() with architecture agnostic arch_phys_wc_add() is complete, this will ensure write-combining implementations (PAT on x86) is taken advantage instead of using MTRR. With the effort done now, hide direct MTRR access for drivers. The legacy user-space /proc/mtrr ABI is not affected. Update x86 documentation on MTRR to reflect the completion of the phasing out of direct access to MTRR, also add a note on platform firmware code use of MTRRs based on the obituary discussion of MTRRs on Linux [0]. [0] http://lkml.kernel.org/r/1438991330.3109.196.camel@hp.com Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com> Cc: <syrjala@sci.fi> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Walls <awalls@md.metrocast.net> Cc: Antonino Daplas <adaplas@gmail.com> Cc: Borislav Petkov <bp@suse.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dave Airlie <airlied@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: Doug Ledford <dledford@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com> Cc: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Suresh Siddha <sbsiddha@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com> Cc: Toshi Kani <toshi.kani@hp.com> Cc: Ville Syrjälä <syrjala@sci.fi> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: airlied@linux.ie Cc: benh@kernel.crashing.org Cc: bhelgaas@google.com Cc: dan.j.williams@intel.com Cc: konrad.wilk@oracle.com Cc: linux-fbdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-media@vger.kernel.org Cc: mst@redhat.com Cc: netdev@vger.kernel.org Cc: vinod.koul@intel.com Cc: xen-devel@lists.xensource.com Link: http://lkml.kernel.org/r/1440443613-13696-12-git-send-email-mcgrof@do-not-panic.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -6,10 +6,22 @@ Luis R. Rodriguez <mcgrof@do-not-panic.com> - April 9, 2015
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===============================================================================
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Phasing out MTRR use
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MTRR use is replaced on modern x86 hardware with PAT. Over time the only type
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of effective MTRR that is expected to be supported will be for write-combining.
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As MTRR use is phased out device drivers should use arch_phys_wc_add() to make
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MTRR effective on non-PAT systems while a no-op on PAT enabled systems.
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MTRR use is replaced on modern x86 hardware with PAT. Direct MTRR use by
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drivers on Linux is now completely phased out, device drivers should use
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arch_phys_wc_add() in combination with ioremap_wc() to make MTRR effective on
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non-PAT systems while a no-op but equally effective on PAT enabled systems.
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Even if Linux does not use MTRRs directly, some x86 platform firmware may still
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set up MTRRs early before booting the OS. They do this as some platform
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firmware may still have implemented access to MTRRs which would be controlled
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and handled by the platform firmware directly. An example of platform use of
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MTRRs is through the use of SMI handlers, one case could be for fan control,
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the platform code would need uncachable access to some of its fan control
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registers. Such platform access does not need any Operating System MTRR code in
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place other than mtrr_type_lookup() to ensure any OS specific mapping requests
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are aligned with platform MTRR setup. If MTRRs are only set up by the platform
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firmware code though and the OS does not make any specific MTRR mapping
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requests mtrr_type_lookup() should always return MTRR_TYPE_INVALID.
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For details refer to Documentation/x86/pat.txt.
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@ -448,7 +448,6 @@ int mtrr_add(unsigned long base, unsigned long size, unsigned int type,
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return mtrr_add_page(base >> PAGE_SHIFT, size >> PAGE_SHIFT, type,
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increment);
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}
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EXPORT_SYMBOL(mtrr_add);
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/**
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* mtrr_del_page - delete a memory type region
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@ -537,7 +536,6 @@ int mtrr_del(int reg, unsigned long base, unsigned long size)
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return -EINVAL;
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return mtrr_del_page(reg, base >> PAGE_SHIFT, size >> PAGE_SHIFT);
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}
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EXPORT_SYMBOL(mtrr_del);
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/**
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* arch_phys_wc_add - add a WC MTRR and handle errors if PAT is unavailable
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