Re: [PATCHv3.1 2.1/2] x86/coco: Add API to handle encryption mask

[Tom Lendacky]

On 2/18/22 18:13, Kirill A. Shutemov wrote:
> AMD SME/SEV uses a bit in the page table entries to indicate that the
> page is encrypted and not accessible to the VMM.
>
> TDX uses a similar approach, but the polarity of the mask is opposite to
> AMD: if the bit is set the page is accessible to VMM.
>
> Provide vendor-neutral API to deal with the mask:
>
>    - cc_mkenc() and cc_mkdec() modify given address to make it
>      encrypted/decrypted. It can be applied to phys_addr_t, pgprotval_t
>      or page table entry value.
>
>    - cc_get_mask() returns encryption or decrypthion mask. It is useful
>      for set_memory_encrypted() and set_memory_decrypted()
>      implementation.
>
> The implementation will be extended to cover TDX.
>
> pgprot_decrypted() is used by drivers (i915, virtio_gpu, vfio).
> cc_mkdec() called by pgprot_decrypted(). Export cc_mkdec().
>
> HyperV doesn't use bits in page table entries, so the mask is 0 for both
> encrypthion and decrypthion.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

> @@ -84,7 +85,39 @@ bool cc_platform_has(enum cc_attr attr)
>   }
>   EXPORT_SYMBOL_GPL(cc_platform_has);
>   
> -__init void cc_init(enum cc_vendor vendor)
> +u64 cc_get_mask(bool enc)

I was a bit confused by this name, expecting to always get the mask, but 
it is dependent on the input parameter. How about cc_get_operation_mask() 
or ... ? I'm struggling to come up with a good name, but plain 
cc_get_mask() is very confusing.

> +{
> +	switch (cc_vendor) {
> +	case CC_VENDOR_AMD:
> +		return enc ? cc_mask : 0;
> +	default:
> +		return 0;
> +	}
> +}
> +

> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index eb7fbd85b77e..fa758247ab57 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -603,5 +603,5 @@ void __init sme_enable(struct boot_params *bp)
>   out:
>   	physical_mask &= ~sme_me_mask;
>   	if (sme_me_mask)
> -		cc_init(CC_VENDOR_AMD);
> +		cc_init(CC_VENDOR_AMD, sme_me_mask);

Since you're adding the if statement, you can probably wrap the adjustment 
to physical_mask within the if, also (I guess in the previous patch). Not 
required, though.

Thanks,
Tom