linux-kernel - Re: [PATCH 19/26] x86/tdx: Make pages shared in ioremap()

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Message-ID: <20211223171530.v73posbqizb5l3md@black.fi.intel.com>
Date:   Thu, 23 Dec 2021 20:15:30 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     tglx@...utronix.de, 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: [PATCH 19/26] x86/tdx: Make pages shared in ioremap()

On Wed, Dec 22, 2021 at 11:26:59AM -0600, Tom Lendacky wrote:
> On 12/14/21 9:02 AM, 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. Introduce CC_ATTR_GUEST_TDX
> > to add TDX-specific changes to the AMD SEV/SME memory encryption 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().
> > 
> 
> > --- a/arch/x86/mm/mem_encrypt.c
> > +++ b/arch/x86/mm/mem_encrypt.c
> > @@ -14,6 +14,33 @@
> >   #include <linux/mem_encrypt.h>
> >   #include <linux/virtio_config.h>
> > +#include <asm/tdx.h>
> > +
> > +/*
> > + * Set or unset encryption attribute in vendor agnostic way.
> > + */
> > +pgprot_t pgprot_cc_encrypted(pgprot_t prot)
> > +{
> > +	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
> > +		return __pgprot(__sme_set(pgprot_val(prot)));
> > +	else if (cc_platform_has(CC_ATTR_GUEST_TDX))
> > +		return __pgprot(pgprot_val(prot) & ~tdx_shared_mask());
> > +
> 
> Hmmm... I believe this breaks SEV guests. __sme_set() uses sme_me_mask which
> is used for both SME and SEV. With the current checks, an SEV guest will end
> up never setting an encrypted address through this path. Ditto below on the
> decrypted path.

Hm, okay. What if I rewrite code like this:

	pgprot_t pgprot_cc_encrypted(pgprot_t prot)
	{
		if (cc_platform_has(CC_ATTR_GUEST_TDX))
			return __pgprot(pgprot_val(prot) & ~tdx_shared_mask());
		else
			return __pgprot(__sme_set(pgprot_val(prot)));
	}

I believe it should cover all cases, right?

-- 
 Kirill A. Shutemov