Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 24 May 2023 01:37:50 +0300
From:   kirill.shutemov@linux.intel.com
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     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,
        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,
        linux-kernel@vger.kernel.org, Tianyu.Lan@microsoft.com
Subject: Re: [PATCH v6 2/6] x86/tdx: Support vmalloc() for
 tdx_enc_status_changed()
Message-ID: <20230523223750.botogigv6ht7p2zg@box.shutemov.name>
References: <20230504225351.10765-1-decui@microsoft.com>
 <20230504225351.10765-3-decui@microsoft.com>
 <9e466079-ff27-f928-b470-eb5ef157f048@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <9e466079-ff27-f928-b470-eb5ef157f048@intel.com>
Precedence: bulk

On Tue, May 23, 2023 at 01:39:11PM -0700, Dave Hansen wrote:
> 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?

Alias processing in __change_page_attr_set_clr() will change direct
mapping if you call it on vmalloc()ed memory. I think we are safe wrt
load_unaligned_zeropad() here.
-- 
  Kiryl Shutsemau / Kirill A. Shutemov