linux-kernel - Re: [RFC v2 28/32] x86/tdx: Make pages shared in ioremap()

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Date:   Wed, 26 May 2021 14:37:39 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...en8.de>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>, linux-kernel@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [RFC v2 28/32] x86/tdx: Make pages shared in ioremap()



On 5/21/21 9:19 AM, Tom Lendacky wrote:
> In arch/x86/mm/mem_encrypt.c, sme_early_init() (should have renamed that
> when SEV support was added), we do:
> 	if (sev_active())
> 		swiotlb_force = SWIOTLB_FORCE;
> 
> TDX should be able to do a similar thing without having to touch
> arch/x86/kernel/pci-swiotlb.c.
> 
> That would remove any confusion over SME being part of a
> protected_guest_has() call.

You mean sme_active() check in arch/x86/kernel/pci-swiotlb.c is redundant?

  41 int __init pci_swiotlb_detect_4gb(void)
  42 {
  43         /* don't initialize swiotlb if iommu=off (no_iommu=1) */
  44         if (!no_iommu && max_possible_pfn > MAX_DMA32_PFN)
  45                 swiotlb = 1;
  46
  47         /*
  48          * If SME is active then swiotlb will be set to 1 so that bounce
  49          * buffers are allocated and used for devices that do not support
  50          * the addressing range required for the encryption mask.
  51          */
  52         if (sme_active() || is_tdx_guest())
  53                 swiotlb = 1;


-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer