linux-kernel - Re: [PATCH v2 2/6] x86/tdx: Support vmalloc() for tdx_enc_status

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Date:   Thu, 5 Jan 2023 20:10:24 +0200
From:   Zhi Wang <zhi.wang.linux@...il.com>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de" <bp@...en8.de>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "zhi.a.wang@...el.com" <zhi.a.wang@...el.com>
Subject: Re: [PATCH v2 2/6] x86/tdx: Support vmalloc() for
 tdx_enc_status_changed()

On Thu, 5 Jan 2023 17:33:16 +0000
Dexuan Cui <decui@...rosoft.com> wrote:

> > From: Zhi Wang <zhi.wang.linux@...il.com>
> > Sent: Thursday, January 5, 2023 1:45 AM
> >  [...]
> > On Tue,  6 Dec 2022 16:33:21 -0800
> > Dexuan Cui <decui@...rosoft.com> 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.
> > 
> > It seems calling set_memory_decrypted() in netvsc_init_buf() is
> > missing in this patch series. I guess there should be another one
> > extra patch to cover that.
> 
> set_memory_decrypted() is not missing here. In netvsc_init_buf(), after
> the line "net_device->recv_buf = vzalloc(buf_size);", we have 
> 
> vmbus_establish_gpadl(device->channel, net_device->recv_buf, ...), which
> 
> calls __vmbus_establish_gpadl(), which calls 
> 
> set_memory_decrypted((unsigned long)kbuffer, ...)
> 

I see. Then do we still need the hv_map_memory()in the following
code piece in netvsc.c after {set_memoery_encrypted, decrypted}()
supporting memory from vmalloc()?

	/* set_memory_decrypted() is called here. */

        ret = vmbus_establish_gpadl(device->channel, net_device->recv_buf,
                                    buf_size,
                                    &net_device->recv_buf_gpadl_handle);
        if (ret != 0) {
                netdev_err(ndev,
                        "unable to establish receive buffer's gpadl\n");
                goto cleanup;
        }
	
	/* Should we remove this? */
        if (hv_isolation_type_snp()) {
                vaddr = hv_map_memory(net_device->recv_buf, buf_size);
                if (!vaddr) {
                        ret = -ENOMEM;
                        goto cleanup;
                }

                net_device->recv_original_buf = net_device->recv_buf;
                net_device->recv_buf = vaddr;
        }

I assume that we need an VA mapped to a shared GPA here.

The VA(net_device->recv_buf) has been associated with a shared GPA in
set_memory_decrypted() by adjusting the kernel page table. hv_map_memory()
is with similar purpose but just a different way:

void *hv_map_memory(void *addr, unsigned long size)
{
        unsigned long *pfns = kcalloc(size / PAGE_SIZE,
                                      sizeof(unsigned long), GFP_KERNEL);
        void *vaddr;
        int i;

        if (!pfns)
                return NULL;

        for (i = 0; i < size / PAGE_SIZE; i++)
                pfns[i] = vmalloc_to_pfn(addr + i * PAGE_SIZE) +
                        (ms_hyperv.shared_gpa_boundary >> PAGE_SHIFT);

        vaddr = vmap_pfn(pfns, size / PAGE_SIZE, PAGE_KERNEL_IO);
        kfree(pfns);

        return vaddr;
}