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Date:   Tue, 23 May 2023 13:39:11 -0700
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Subject: Re: [PATCH v6 2/6] x86/tdx: Support vmalloc() for
 tdx_enc_status_changed()
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To:     Dexuan Cui <decui@microsoft.com>, ak@linux.intel.com,
        arnd@arndb.de, bp@alien8.de, brijesh.singh@amd.com,
        dan.j.williams@intel.com, dave.hansen@linux.intel.com,
        haiyangz@microsoft.com, hpa@zytor.com, jane.chu@oracle.com,
        kirill.shutemov@linux.intel.com, kys@microsoft.com,
        linux-arch@vger.kernel.org, linux-hyperv@vger.kernel.org,
        luto@kernel.org, mingo@redhat.com, peterz@infradead.org,
        rostedt@goodmis.org, sathyanarayanan.kuppuswamy@linux.intel.com,
        seanjc@google.com, tglx@linutronix.de, tony.luck@intel.com,
        wei.liu@kernel.org, x86@kernel.org, mikelley@microsoft.com
Cc:     linux-kernel@vger.kernel.org, Tianyu.Lan@microsoft.com
References: <20230504225351.10765-1-decui@microsoft.com>
 <20230504225351.10765-3-decui@microsoft.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20230504225351.10765-3-decui@microsoft.com>
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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?