linux-kernel - Re: [RFC PATCH v2 15/20] iommu/amd: AMD IOMMU support for memory encryption

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Date:   Mon, 12 Sep 2016 13:45:50 +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,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 15/20] iommu/amd: AMD IOMMU support for memory
 encryption

On Mon, Aug 22, 2016 at 05:38:20PM -0500, Tom Lendacky wrote:
> Add support to the AMD IOMMU driver to set the memory encryption mask if
> memory encryption is enabled.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/include/asm/mem_encrypt.h |    2 ++
>  arch/x86/mm/mem_encrypt.c          |    5 +++++
>  drivers/iommu/amd_iommu.c          |   10 ++++++++++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 384fdfb..e395729 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -36,6 +36,8 @@ void __init sme_early_init(void);
>  /* Architecture __weak replacement functions */
>  void __init mem_encrypt_init(void);
>  
> +unsigned long amd_iommu_get_me_mask(void);
> +
>  unsigned long swiotlb_get_me_mask(void);
>  void swiotlb_set_mem_dec(void *vaddr, unsigned long size);
>  
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 6b2e8bf..2f28d87 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -185,6 +185,11 @@ void __init mem_encrypt_init(void)
>  	swiotlb_clear_encryption();
>  }
>  
> +unsigned long amd_iommu_get_me_mask(void)
> +{
> +	return sme_me_mask;
> +}
> +
>  unsigned long swiotlb_get_me_mask(void)
>  {
>  	return sme_me_mask;
> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> index 96de97a..63995e3 100644
> --- a/drivers/iommu/amd_iommu.c
> +++ b/drivers/iommu/amd_iommu.c
> @@ -166,6 +166,15 @@ struct dma_ops_domain {
>  static struct iova_domain reserved_iova_ranges;
>  static struct lock_class_key reserved_rbtree_key;
>  
> +/*
> + * Support for memory encryption. If memory encryption is supported, then an
> + * override to this function will be provided.
> + */
> +unsigned long __weak amd_iommu_get_me_mask(void)
> +{
> +	return 0;
> +}

So instead of adding a function each time which returns sme_me_mask
for each user it has, why don't you add a single function which
returns sme_me_mask in mem_encrypt.c and add an inline in the header
mem_encrypt.h which returns 0 for the !CONFIG_AMD_MEM_ENCRYPT case.

This all is still funny because we access sme_me_mask directly for the
different KERNEL_* masks but then you're adding an accessor function.

So what you should do instead, IMHO, is either hide sme_me_mask
altogether and use the accessor functions only (not sure if that would
work in all cases) or expose sme_me_mask unconditionally and have it be
0 if CONFIG_AMD_MEM_ENCRYPT is not enabled so that it just works.

Or is there a third, more graceful variant?

-- 
Regards/Gruss,
    Boris.

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