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

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Date:   Thu, 1 Apr 2021 13:26:23 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     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 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?  I was
somehow expecting that we would need to do this for some host<->guest
communication pages.

>  static unsigned int __ioremap_check_encrypted(struct resource *res)
>  {
> -	if (!sev_active())
> +	if (!sev_active() && !is_tdx_guest())
>  		return 0;
>  
>  	switch (res->desc) {
> @@ -244,6 +244,8 @@ __ioremap_caller(resource_size_t phys_addr, unsigned long size,
>  	prot = PAGE_KERNEL_IO;
>  	if ((io_desc.flags & IORES_MAP_ENCRYPTED) || encrypted)
>  		prot = pgprot_encrypted(prot);
> +	else if (is_tdx_guest())
> +		prot = pgprot_tdx_shared(prot);