linux-kernel - Re: [PATCH v2 04/19] powerpc/kvm: Prefer fault_in_pages

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Message-ID: <20180329181838.Horde.opfAaSRmEf1pJwACgzIcVg8@messagerie.si.c-s.fr>
Date:   Thu, 29 Mar 2018 18:18:38 +0200
From:   LEROY Christophe <christophe.leroy@....fr>
To:     Mathieu Malaterre <malat@...ian.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm-ppc@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...abs.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v2 04/19] powerpc/kvm: Prefer fault_in_pages_readable
 function

Mathieu Malaterre <malat@...ian.org> a écrit :

> Directly use fault_in_pages_readable instead of manual __get_user code. Fix
> warning treated as error with W=1:
>
>   arch/powerpc/kernel/kvm.c:675:6: error: variable ‘tmp’ set but not  
> used [-Werror=unused-but-set-variable]
>
> Suggested-by: Christophe Leroy <christophe.leroy@....fr>
> Signed-off-by: Mathieu Malaterre <malat@...ian.org>

Reviewed-by: Christophe Leroy <christophe.leroy@....fr>

> ---
> v2: use fault_in_pages_readable instead
>  arch/powerpc/kernel/kvm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kvm.c b/arch/powerpc/kernel/kvm.c
> index 9ad37f827a97..124c51030b75 100644
> --- a/arch/powerpc/kernel/kvm.c
> +++ b/arch/powerpc/kernel/kvm.c
> @@ -25,6 +25,7 @@
>  #include <linux/kvm_para.h>
>  #include <linux/slab.h>
>  #include <linux/of.h>
> +#include <linux/pagemap.h>
>
>  #include <asm/reg.h>
>  #include <asm/sections.h>
> @@ -672,14 +673,13 @@ static void kvm_use_magic_page(void)
>  {
>  	u32 *p;
>  	u32 *start, *end;
> -	u32 tmp;
>  	u32 features;
>
>  	/* Tell the host to map the magic page to -4096 on all CPUs */
>  	on_each_cpu(kvm_map_magic_page, &features, 1);
>
>  	/* Quick self-test to see if the mapping works */
> -	if (__get_user(tmp, (u32*)KVM_MAGIC_PAGE)) {
> +	if (!fault_in_pages_readable((const char *)KVM_MAGIC_PAGE, sizeof(u32))) {
>  		kvm_patching_worked = false;
>  		return;
>  	}
> --
> 2.11.0