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From:   Andreas Gruenbacher <agruenba@redhat.com>
Date:   Mon, 15 Nov 2021 18:47:41 +0100
Message-ID: <CAHc6FU7a+gTDCZMCE6gOH1EDUW5SghPbQbsbeVtdg4tV1VdGxg@mail.gmail.com>
Subject: Re: [PATCH 5.4 063/355] powerpc/kvm: Fix kvm_use_magic_page
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>
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Greg,

On Mon, Nov 15, 2021 at 6:10 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> From: Andreas Gruenbacher <agruenba@redhat.com>
>
> commit 0c8eb2884a42d992c7726539328b7d3568f22143 upstream.
>
> When switching from __get_user to fault_in_pages_readable, commit
> 9f9eae5ce717 broke kvm_use_magic_page: like __get_user,
> fault_in_pages_readable returns 0 on success.

I've not heard back from the maintainers about this patch so far, so
it would probably be safer to leave it out of stable for now.

Thanks,
Andreas

> Fixes: 9f9eae5ce717 ("powerpc/kvm: Prefer fault_in_pages_readable function")
> Cc: stable@vger.kernel.org # v4.18+
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  arch/powerpc/kernel/kvm.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/arch/powerpc/kernel/kvm.c
> +++ b/arch/powerpc/kernel/kvm.c
> @@ -669,7 +669,7 @@ static void __init kvm_use_magic_page(vo
>         on_each_cpu(kvm_map_magic_page, &features, 1);
>
>         /* Quick self-test to see if the mapping works */
> -       if (!fault_in_pages_readable((const char *)KVM_MAGIC_PAGE, sizeof(u32))) {
> +       if (fault_in_pages_readable((const char *)KVM_MAGIC_PAGE, sizeof(u32))) {
>                 kvm_patching_worked = false;
>                 return;
>         }
>
>