Re: [PATCH v14 04/10] set_memory: allow querying whether set_direct_map_*() is actually enabled

From: Mike Rapoport <rppt@linux.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christopher Lameter <cl@linux.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	David Hildenbrand <david@redhat.com>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
	Shuah Khan <shuah@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
	linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
	x86@kernel.org
Subject: Re: [PATCH v14 04/10] set_memory: allow querying whether set_direct_map_*() is actually enabled
Date: Sun, 6 Dec 2020 13:28:26 +0200	[thread overview]
Message-ID: <20201206112826.GB123287@linux.ibm.com> (raw)
In-Reply-To: <20201203153610.724f40f26ca1620247bc6b09@linux-foundation.org>

On Thu, Dec 03, 2020 at 03:36:10PM -0800, Andrew Morton wrote:
> On Thu,  3 Dec 2020 08:29:43 +0200 Mike Rapoport <rppt@kernel.org> wrote:
> 
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > On arm64, set_direct_map_*() functions may return 0 without actually
> > changing the linear map. This behaviour can be controlled using kernel
> > parameters, so we need a way to determine at runtime whether calls to
> > set_direct_map_invalid_noflush() and set_direct_map_default_noflush() have
> > any effect.
> > 
> > Extend set_memory API with can_set_direct_map() function that allows
> > checking if calling set_direct_map_*() will actually change the page table,
> > replace several occurrences of open coded checks in arm64 with the new
> > function and provide a generic stub for architectures that always modify
> > page tables upon calls to set_direct_map APIs.
> > 
> > ...
> >
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -22,6 +22,7 @@
> >  #include <linux/io.h>
> >  #include <linux/mm.h>
> >  #include <linux/vmalloc.h>
> > +#include <linux/set_memory.h>
> >  
> >  #include <asm/barrier.h>
> >  #include <asm/cputype.h>
> > @@ -477,7 +478,7 @@ static void __init map_mem(pgd_t *pgdp)
> >  	int flags = 0;
> >  	u64 i;
> >  
> > -	if (rodata_full || debug_pagealloc_enabled())
> > +	if (can_set_direct_map())
> >  		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
> 
> Changes in -next turned this into
> 
> 	if (can_set_direct_map() || crash_mem_map)

Thanks for updating!

-- 
Sincerely yours,
Mike.