linux-kernel - Re: [RFC v1 23/26] x86/tdx: Make pages shared in ioremap()

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Date:   Tue, 6 Apr 2021 19:00:16 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v1 23/26] x86/tdx: Make pages shared in ioremap()

On Thu, Apr 01, 2021 at 01:26:23PM -0700, Dave Hansen wrote:
> On 2/5/21 3:38 PM, Kuppuswamy Sathyanarayanan wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > 
> > All ioremap()ed paged that are not backed by normal memory (NONE or
> > RESERVED) have to be mapped as shared.
> 
> s/paged/pages/
> 
> 
> > +/* Make the page accesable by VMM */
> > +#define pgprot_tdx_shared(prot) __pgprot(pgprot_val(prot) | tdx_shared_mask())
> > +
> >  #ifndef __ASSEMBLY__
> >  #include <asm/x86_init.h>
> >  #include <asm/fpu/xstate.h>
> > diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> > index 9e5ccc56f8e0..a0ba760866d4 100644
> > --- a/arch/x86/mm/ioremap.c
> > +++ b/arch/x86/mm/ioremap.c
> > @@ -87,12 +87,12 @@ static unsigned int __ioremap_check_ram(struct resource *res)
> >  }
> >  
> >  /*
> > - * In a SEV guest, NONE and RESERVED should not be mapped encrypted because
> > - * there the whole memory is already encrypted.
> > + * In a SEV or TDX guest, NONE and RESERVED should not be mapped encrypted (or
> > + * private in TDX case) because there the whole memory is already encrypted.
> >   */
> 
> But doesn't this mean that we can't ioremap() normal memory?

It's not allowed anyway: see (io_desc.flags & IORES_MAP_SYSTEM_RAM) in the
__ioremap_caller().


> I was somehow expecting that we would need to do this for some
> host<->guest communication pages.

It goes though DMA API, not ioremap().

-- 
 Kirill A. Shutemov