Re: [RFC PATCH v4 07/28] x86: Provide general kernel support for memory encryption

From: Tom Lendacky
Date: Thu Feb 23 2017 - 18:17:04 EST

On 2/22/2017 12:13 PM, Dave Hansen wrote:
On 02/16/2017 07:43 AM, Tom Lendacky wrote:
static inline unsigned long pte_pfn(pte_t pte)
- return (pte_val(pte) & PTE_PFN_MASK) >> PAGE_SHIFT;
+ return (pte_val(pte) & ~sme_me_mask & PTE_PFN_MASK) >> PAGE_SHIFT;

static inline unsigned long pmd_pfn(pmd_t pmd)
- return (pmd_val(pmd) & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;
+ return (pmd_val(pmd) & ~sme_me_mask & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;

Could you talk a bit about why you chose to do the "~sme_me_mask" bit in
here instead of making it a part of PTE_PFN_MASK / pmd_pfn_mask(pmd)?

I think that's a good catch. Let me look at it, but I believe that it
should be possible to do and avoid what you're worried about below.


It might not matter, but I'd be worried that this ends up breaking
direct users of PTE_PFN_MASK / pmd_pfn_mask(pmd) since they now no
longer mask the PFN out of a PTE.