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SubjectRe: [PATCHv3.1 2.1/2] x86/coco: Add API to handle encryption mask
From
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@linux.intel.com>

> @@ -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

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