linux-kernel - Re: [PATCH v6 2/6] x86/tdx: Support vmalloc() for tdx_enc_status

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Message-ID: <9e466079-ff27-f928-b470-eb5ef157f048@intel.com>
Date:   Tue, 23 May 2023 13:39:11 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Dexuan Cui <decui@...rosoft.com>, ak@...ux.intel.com,
        arnd@...db.de, bp@...en8.de, brijesh.singh@....com,
        dan.j.williams@...el.com, dave.hansen@...ux.intel.com,
        haiyangz@...rosoft.com, hpa@...or.com, jane.chu@...cle.com,
        kirill.shutemov@...ux.intel.com, kys@...rosoft.com,
        linux-arch@...r.kernel.org, linux-hyperv@...r.kernel.org,
        luto@...nel.org, mingo@...hat.com, peterz@...radead.org,
        rostedt@...dmis.org, sathyanarayanan.kuppuswamy@...ux.intel.com,
        seanjc@...gle.com, tglx@...utronix.de, tony.luck@...el.com,
        wei.liu@...nel.org, x86@...nel.org, mikelley@...rosoft.com
Cc:     linux-kernel@...r.kernel.org, Tianyu.Lan@...rosoft.com
Subject: Re: [PATCH v6 2/6] x86/tdx: Support vmalloc() for
 tdx_enc_status_changed()

On 5/4/23 15:53, Dexuan Cui wrote:
> When a TDX guest runs on Hyper-V, the hv_netvsc driver's netvsc_init_buf()
> allocates buffers using vzalloc(), and needs to share the buffers with the
> host OS by calling set_memory_decrypted(), which is not working for
> vmalloc() yet. Add the support by handling the pages one by one.

I think this sets a bad precedent.

There are consequences for converting pages between shared and private.
Doing it on a vmalloc() mapping is guaranteed to fracture the underlying
EPT/SEPT mappings.

How does this work with load_unaligned_zeropad()?  Couldn't it be
running around poking at one of these vmalloc()'d pages via the direct
map during a shared->private conversion before the page has been accepted?