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

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  Re: [RFC PATCH v2 15/20] iommu/amd: AMD IOMMU support for memory  encryption Borislav Petkov <bp@alien8.de> - 2016-09-12 13:50 +0200
    Re: [RFC PATCH v2 15/20] iommu/amd: AMD IOMMU support for memory  encryption Borislav Petkov <bp@alien8.de> - 2016-09-14 16:50 +0200
      Re: [RFC PATCH v2 15/20] iommu/amd: AMD IOMMU support for memory  encryption Borislav Petkov <bp@alien8.de> - 2016-09-16 09:10 +0200

#1481172 — 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@amd.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.

ECO tip #101: Trim your mails when you reply.

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#1483403

On Wed, Sep 14, 2016 at 08:45:44AM -0500, Tom Lendacky wrote:
> Currently, mem_encrypt.h only lives in the arch/x86 directory so it
> wouldn't be able to be included here without breaking other archs.

I'm wondering if it would be simpler to move only sme_me_mask to an
arch-agnostic header just so that we save us all the code duplication.

Hmmm.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--

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#1484708

On Thu, Sep 15, 2016 at 11:57:41AM -0500, Tom Lendacky wrote:
> If I do that, then I could put an #ifdef in the header to include the
> asm/mem_encrypt.h if the memory encryption is configured, else set the
> value to zero.

Yeah, something along those lines...

> I'll look into this. One immediate question becomes do we keep the
> name very specific vs. making it more generic, sme_me_mask vs me_mask,
> etc.

No strong opinion either way from me. My angle is that whatever it is,
we can always rename it later if we decide to.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--

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