linux-kernel - Re: [PATCHv2 22/29] x86/tdx: Make pages shared in ioremap()

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Date:   Wed, 2 Feb 2022 22:27:10 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 22/29] x86/tdx: Make pages shared in ioremap()

On Wed, Feb 02, 2022 at 01:25:28AM +0100, Thomas Gleixner wrote:
> On Mon, Jan 24 2022 at 18:02, Kirill A. Shutemov wrote:
> 
> > In TDX guests, guest memory is protected from host access. If a guest
> > performs I/O, it needs to explicitly share the I/O memory with the host.
> >
> > Make all ioremap()ed pages that are not backed by normal memory
> > (IORES_DESC_NONE or IORES_DESC_RESERVED) mapped as shared.
> >
> > Since TDX memory encryption support is similar to AMD SEV architecture,
> > reuse the infrastructure from AMD SEV code.
> >
> > Add tdx_shared_mask() interface to get the TDX guest shared bitmask.
> >
> > pgprot_decrypted() is used by drivers (i915, virtio_gpu, vfio). Export
> > both pgprot_encrypted() and pgprot_decrypted().
> 
> How so?
> 
> # git grep pgprot_encrypted
> arch/x86/include/asm/pgtable.h:#define pgprot_encrypted(prot)   __pgprot(__sme_set(pgprot_val(prot)))
> arch/x86/mm/ioremap.c:          prot = pgprot_encrypted(prot);
> arch/x86/mm/ioremap.c:  return encrypted_prot ? pgprot_encrypted(prot)
> arch/x86/mm/mem_encrypt_amd.c:          protection_map[i] = pgprot_encrypted(protection_map[i]);
> arch/x86/mm/pat/set_memory.c:           cpa.mask_clr = pgprot_encrypted(cpa.mask_clr);
> arch/x86/platform/efi/quirks.c:                           pgprot_val(pgprot_encrypted(FIXMAP_PAGE_NORMAL)));
> fs/proc/vmcore.c:       prot = pgprot_encrypted(prot);
> include/linux/pgtable.h:#ifndef pgprot_encrypted
> include/linux/pgtable.h:#define pgprot_encrypted(prot)  (prot)
> 
> I cannot find any of the above mentioned subsystems in this grep
> output. Neither does this patch add any users which require those
> exports.

Try to grep pgprot_decrypted().

I guess we can get away not exporting pgprot_encrypted(), but this
asymmetry bothers me :)

-- 
 Kirill A. Shutemov