linux-kernel - Re: [PATCHv3.1 2.1/2] x86/coco: Add API to handle encryption mask

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Message-ID: <20220221221049.p5zvappg4s2mjem7@black.fi.intel.com>
Date:   Tue, 22 Feb 2022 01:10:49 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com,
        dave.hansen@...el.com, david@...hat.com, hpa@...or.com,
        jgross@...e.com, jmattson@...gle.com, joro@...tes.org,
        jpoimboe@...hat.com, knsathya@...nel.org,
        linux-kernel@...r.kernel.org, luto@...nel.org, mingo@...hat.com,
        pbonzini@...hat.com, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, sdeep@...are.com,
        seanjc@...gle.com, tglx@...utronix.de, tony.luck@...el.com,
        vkuznets@...hat.com, wanpengli@...cent.com, x86@...nel.org
Subject: Re: [PATCHv3.1 2.1/2] x86/coco: Add API to handle encryption mask

On Mon, Feb 21, 2022 at 10:05:20PM +0100, Borislav Petkov wrote:
> On Sat, Feb 19, 2022 at 03:13:05AM +0300, 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
> 
> Unknown word [encrypthion] in commit message.
> Suggestions: ['encryption', 'decryption']
> 
> Unknown word [decrypthion] in commit message.
> Suggestions: ['decryption', 'encryption']

Ughh. Sorry. Will fix.

> > 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);
> 
> I'm wondering why this is looking weird... an init function with two
> arguments which get assigned. I think it would be better if you do:
> 
> 	cc_set_vendor(CC_VENDOR_XXX);
> 	cc_set_mask(mask);
> 
> and those helpers simply assign to __ro_after_init, local variables.
> 
> IOW, simple setter functions.

I'm not sure it is a good idea. It leaves room for code between these two
calls. I believe they conceptually has to initialized in one shot. That's
the only way we get consistent state.

-- 
 Kirill A. Shutemov