linux-kernel - Re: [PATCH v7 31/36] x86/mm, kexec: Allow kexec to be used with SME

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Date:   Fri, 23 Jun 2017 10:56:07 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, xen-devel@...ts.xen.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Brijesh Singh <brijesh.singh@....com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Alexander Potapenko <glider@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dave Young <dyoung@...hat.com>, Rik van Riel <riel@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7 31/36] x86/mm, kexec: Allow kexec to be used with SME

On Fri, Jun 16, 2017 at 01:55:45PM -0500, Tom Lendacky wrote:
> Provide support so that kexec can be used to boot a kernel when SME is
> enabled.
> 
> Support is needed to allocate pages for kexec without encryption.  This
> is needed in order to be able to reboot in the kernel in the same manner
> as originally booted.
> 
> Additionally, when shutting down all of the CPUs we need to be sure to
> flush the caches and then halt. This is needed when booting from a state
> where SME was not active into a state where SME is active (or vice-versa).
> Without these steps, it is possible for cache lines to exist for the same
> physical location but tagged both with and without the encryption bit. This
> can cause random memory corruption when caches are flushed depending on
> which cacheline is written last.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/include/asm/init.h          |    1 +
>  arch/x86/include/asm/kexec.h         |    8 ++++++++
>  arch/x86/include/asm/pgtable_types.h |    1 +
>  arch/x86/kernel/machine_kexec_64.c   |   22 +++++++++++++++++++++-
>  arch/x86/kernel/process.c            |   17 +++++++++++++++--
>  arch/x86/mm/ident_map.c              |   12 ++++++++----
>  include/linux/kexec.h                |   14 ++++++++++++++
>  kernel/kexec_core.c                  |   12 +++++++++++-
>  8 files changed, 79 insertions(+), 8 deletions(-)

...

> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index c9481eb..5d17fd6 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -334,6 +334,20 @@ static inline void *boot_phys_to_virt(unsigned long entry)
>  	return phys_to_virt(boot_phys_to_phys(entry));
>  }
>  
> +#ifndef arch_kexec_post_alloc_pages
> +static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages,
> +					      gfp_t gfp)
> +{
> +	return 0;
> +}
> +#endif

Just a nitpick:

static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, gfp_t gfp) { return 0; }
static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) { }

Other than that:

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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