From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Dave Hansen <dave.hansen@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
Kai Huang <kai.huang@linux.intel.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv5 09/19] x86/mm: Preserve KeyID on pte_modify() and pgprot_modify()
Date: Fri, 20 Jul 2018 15:42:56 +0300 [thread overview]
Message-ID: <20180720124256.nvtw4mw2lcjkfrte@kshutemo-mobl1> (raw)
In-Reply-To: <202c809d-8720-8dbb-51f5-1018e947a62a@intel.com>
On Wed, Jul 18, 2018 at 04:30:35PM -0700, Dave Hansen wrote:
> On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> > An encrypted VMA will have KeyID stored in vma->vm_page_prot. This way
> > we don't need to do anything special to setup encrypted page table
> > entries
>
> We don't do anything special for protection keys, either. They just
> work too.
>
> > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> > index 99fff853c944..3731f7e08757 100644
> > --- a/arch/x86/include/asm/pgtable_types.h
> > +++ b/arch/x86/include/asm/pgtable_types.h
> > @@ -120,8 +120,21 @@
> > * protection key is treated like _PAGE_RW, for
> > * instance, and is *not* included in this mask since
> > * pte_modify() does modify it.
> > + *
> > + * They include the physical address and the memory encryption keyID.
> > + * The paddr and the keyID never occupy the same bits at the same time.
> > + * But, a given bit might be used for the keyID on one system and used for
> > + * the physical address on another. As an optimization, we manage them in
> > + * one unit here since their combination always occupies the same hardware
> > + * bits. PTE_PFN_MASK_MAX stores combined mask.
> > + *
> > + * Cast PAGE_MASK to a signed type so that it is sign-extended if
> > + * virtual addresses are 32-bits but physical addresses are larger
> > + * (ie, 32-bit PAE).
> > */
>
> Could you please make the comment block consistent? You're a lot wider
> than the comment above.
Okay.
> > -#define _PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
> > +#define PTE_PFN_MASK_MAX \
> > + (((signed long)PAGE_MASK) & ((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
> > +#define _PAGE_CHG_MASK (PTE_PFN_MASK_MAX | _PAGE_PCD | _PAGE_PWT | \
> > _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY | \
> > _PAGE_SOFT_DIRTY)
>
> Man, I'm not a fan of this. This saves us from consuming 6 VM_HIGH bits
> (which we are not short on). But, at the cost of complexity.
15, not 6. We have up-to 15 KeyID bits architecturally.
We can just have a separate field in vm_area_struct if we must.
But vm_page_prot work fine so far. I don't see a big reasone to change
them.
> Protection keys eat up PTE space and have an interface called
> pkey_mprotect(). MKTME KeyIDs take up PTE space and will probably have
> an interface called something_mprotect(). Yet, the implementations are
> going to be _very_ different with pkeys being excluded from
> _PAGE_CHG_MASK and KeyIDs being included.
>
> I think you're saved here because we don't _actually_ do pte_modify() on
> an existing PTE: we blow the old one away upon encrypted_mprotect() and
> replace the PTE with a new one.
>
> But, this is incompatible with any case where we want to change the
> KeyID and keep the old PTE target. With AES-XTS, I guess this is a safe
> assumption, but it's worrying.
>
> Are there scenarios where we want to keep PTE contents, but change the
> KeyID?
I don't see such scenario.
If for some reason we would need to map the same memory with different
KeyID it can be done from scratch. Without modifing existing mapping.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2018-07-20 12:49 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-17 11:20 [PATCHv5 00/19] MKTME enabling Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 01/19] mm: Do no merge VMAs with different encryption KeyIDs Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 02/19] mm: Do not use zero page in encrypted pages Kirill A. Shutemov
2018-07-18 17:36 ` Dave Hansen
2018-07-19 7:16 ` Kirill A. Shutemov
2018-07-19 13:58 ` Dave Hansen
2018-07-20 12:16 ` Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 03/19] mm/ksm: Do not merge pages with different KeyIDs Kirill A. Shutemov
2018-07-18 17:38 ` Dave Hansen
2018-07-19 7:32 ` Kirill A. Shutemov
2018-07-19 14:02 ` Dave Hansen
2018-07-20 12:23 ` Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 04/19] mm/page_alloc: Unify alloc_hugepage_vma() Kirill A. Shutemov
2018-07-18 17:43 ` Dave Hansen
2018-07-17 11:20 ` [PATCHv5 05/19] mm/page_alloc: Handle allocation for encrypted memory Kirill A. Shutemov
2018-07-18 23:03 ` Dave Hansen
2018-07-19 8:27 ` Kirill A. Shutemov
2018-07-19 14:05 ` Dave Hansen
2018-07-20 12:25 ` Kirill A. Shutemov
2018-07-26 14:25 ` Michal Hocko
2018-07-17 11:20 ` [PATCHv5 06/19] mm/khugepaged: Handle encrypted pages Kirill A. Shutemov
2018-07-18 23:11 ` Dave Hansen
2018-07-19 8:59 ` Kirill A. Shutemov
2018-07-19 14:13 ` Dave Hansen
2018-07-20 12:29 ` Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 07/19] x86/mm: Mask out KeyID bits from page table entry pfn Kirill A. Shutemov
2018-07-18 23:13 ` Dave Hansen
2018-07-19 9:54 ` Kirill A. Shutemov
2018-07-19 14:19 ` Dave Hansen
2018-07-20 12:31 ` Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 08/19] x86/mm: Introduce variables to store number, shift and mask of KeyIDs Kirill A. Shutemov
2018-07-18 23:19 ` Dave Hansen
2018-07-19 10:21 ` Kirill A. Shutemov
2018-07-19 12:37 ` Thomas Gleixner
2018-07-19 13:12 ` Kirill A. Shutemov
2018-07-19 13:18 ` Thomas Gleixner
2018-07-19 13:23 ` Kirill A. Shutemov
2018-07-19 13:40 ` Thomas Gleixner
2018-07-20 12:34 ` Kirill A. Shutemov
2018-07-20 13:17 ` Thomas Gleixner
2018-07-20 13:40 ` Kirill A. Shutemov
2018-07-19 14:23 ` Dave Hansen
2018-07-20 12:34 ` Kirill A. Shutemov
2018-07-31 0:08 ` Kai Huang
2018-07-17 11:20 ` [PATCHv5 09/19] x86/mm: Preserve KeyID on pte_modify() and pgprot_modify() Kirill A. Shutemov
2018-07-18 23:30 ` Dave Hansen
2018-07-20 12:42 ` Kirill A. Shutemov [this message]
2018-07-17 11:20 ` [PATCHv5 10/19] x86/mm: Implement page_keyid() using page_ext Kirill A. Shutemov
2018-07-18 23:38 ` Dave Hansen
2018-07-23 9:45 ` Kirill A. Shutemov
2018-07-23 17:22 ` Alison Schofield
2018-07-17 11:20 ` [PATCHv5 11/19] x86/mm: Implement vma_keyid() Kirill A. Shutemov
2018-07-18 23:40 ` Dave Hansen
2018-07-23 9:47 ` Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 12/19] x86/mm: Implement prep_encrypted_page() and arch_free_page() Kirill A. Shutemov
2018-07-18 23:53 ` Dave Hansen
2018-07-23 9:50 ` Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 13/19] x86/mm: Rename CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 14/19] x86/mm: Allow to disable MKTME after enumeration Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 15/19] x86/mm: Detect MKTME early Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 16/19] x86/mm: Calculate direct mapping size Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 17/19] x86/mm: Implement sync_direct_mapping() Kirill A. Shutemov
2018-07-19 0:01 ` Dave Hansen
2018-07-23 10:04 ` Kirill A. Shutemov
2018-07-23 12:25 ` Dave Hansen
2018-07-17 11:20 ` [PATCHv5 18/19] x86/mm: Handle encrypted memory in page_to_virt() and __pa() Kirill A. Shutemov
2018-07-18 22:21 ` Thomas Gleixner
2018-07-23 10:12 ` Kirill A. Shutemov
2018-07-26 17:26 ` Dave Hansen
2018-07-27 13:49 ` Kirill A. Shutemov
2018-07-17 11:20 ` [PATCHv5 19/19] x86: Introduce CONFIG_X86_INTEL_MKTME Kirill A. Shutemov
2018-08-15 7:48 ` Pavel Machek
2018-08-17 9:24 ` Kirill A. Shutemov
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