linux-kernel - Re: [PATCH v14 04/10] set_memory: allow querying whether set_direct_map

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Date:   Thu, 3 Dec 2020 15:36:10 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org
Subject: Re: [PATCH v14 04/10] set_memory: allow querying whether
 set_direct_map_*() is actually enabled

On Thu,  3 Dec 2020 08:29:43 +0200 Mike Rapoport <rppt@...nel.org> wrote:

> From: Mike Rapoport <rppt@...ux.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)