Drivers: hv: vmbus: Bring the post_msg_page back for TDX VMs with the paravisor

The post_msg_page was removed in
commit 9a6b1a170ca8 ("Drivers: hv: vmbus: Remove the per-CPU post_msg_page")

However, it turns out that we need to bring it back, but only for a TDX VM
with the paravisor: in such a VM, the hyperv_pcpu_input_arg is not decrypted,
but the HVCALL_POST_MESSAGE in such a VM needs a decrypted page as the
hypercall input page: see the comments in hyperv_init() for a detailed
explanation.

Except for HVCALL_POST_MESSAGE and HVCALL_SIGNAL_EVENT, the other hypercalls
in a TDX VM with the paravisor still use hv_hypercall_pg and must use the
hyperv_pcpu_input_arg (which is encrypted in such a VM), when a hypercall
input page is used.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230824080712.30327-8-decui@microsoft.com

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index eca5c4b..3729eee 100644 (file)
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -480,6 +480,22 @@ void __init hyperv_init(void)
         * Setup the hypercall page and enable hypercalls.
         * 1. Register the guest ID
         * 2. Enable the hypercall and register the hypercall page
+        *
+        * A TDX VM with no paravisor only uses TDX GHCI rather than hv_hypercall_pg:
+        * when the hypercall input is a page, such a VM must pass a decrypted
+        * page to Hyper-V, e.g. hv_post_message() uses the per-CPU page
+        * hyperv_pcpu_input_arg, which is decrypted if no paravisor is present.
+        *
+        * A TDX VM with the paravisor uses hv_hypercall_pg for most hypercalls,
+        * which are handled by the paravisor and the VM must use an encrypted
+        * input page: in such a VM, the hyperv_pcpu_input_arg is encrypted and
+        * used in the hypercalls, e.g. see hv_mark_gpa_visibility() and
+        * hv_arch_irq_unmask(). Such a VM uses TDX GHCI for two hypercalls:
+        * 1. HVCALL_SIGNAL_EVENT: see vmbus_set_event() and _hv_do_fast_hypercall8().
+        * 2. HVCALL_POST_MESSAGE: the input page must be a decrypted page, i.e.
+        * hv_post_message() in such a VM can't use the encrypted hyperv_pcpu_input_arg;
+        * instead, hv_post_message() uses the post_msg_page, which is decrypted
+        * in such a VM and is only used in such a VM.
         */
        guest_id = hv_generate_guest_id(LINUX_VERSION_CODE);
        wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
@@ -487,8 +503,8 @@ void __init hyperv_init(void)
        /* Hyper-V requires to write guest os id via ghcb in SNP IVM. */
        hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, guest_id);
 
-       /* A TDX guest uses the GHCI call rather than hv_hypercall_pg. */
-       if (hv_isolation_type_tdx())
+       /* A TDX VM with no paravisor only uses TDX GHCI rather than hv_hypercall_pg */
+       if (hv_isolation_type_tdx() && !ms_hyperv.paravisor_present)
                goto skip_hypercall_pg_init;
 
        hv_hypercall_pg = __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START,

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 48b1623..523c5d9 100644 (file)
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -57,20 +57,37 @@ int hv_post_message(union hv_connection_id connection_id,
 
        local_irq_save(flags);
 
-       aligned_msg = *this_cpu_ptr(hyperv_pcpu_input_arg);
+       /*
+        * A TDX VM with the paravisor must use the decrypted post_msg_page: see
+        * the comment in struct hv_per_cpu_context. A SNP VM with the paravisor
+        * can use the encrypted hyperv_pcpu_input_arg because it copies the
+        * input into the GHCB page, which has been decrypted by the paravisor.
+        */
+       if (hv_isolation_type_tdx() && ms_hyperv.paravisor_present)
+               aligned_msg = this_cpu_ptr(hv_context.cpu_context)->post_msg_page;
+       else
+               aligned_msg = *this_cpu_ptr(hyperv_pcpu_input_arg);
+
        aligned_msg->connectionid = connection_id;
        aligned_msg->reserved = 0;
        aligned_msg->message_type = message_type;
        aligned_msg->payload_size = payload_size;
        memcpy((void *)aligned_msg->payload, payload, payload_size);
 
-       if (hv_isolation_type_snp())
-               status = hv_ghcb_hypercall(HVCALL_POST_MESSAGE,
-                               (void *)aligned_msg, NULL,
-                               sizeof(*aligned_msg));
-       else
+       if (ms_hyperv.paravisor_present) {
+               if (hv_isolation_type_tdx())
+                       status = hv_tdx_hypercall(HVCALL_POST_MESSAGE,
+                                                 virt_to_phys(aligned_msg), 0);
+               else if (hv_isolation_type_snp())
+                       status = hv_ghcb_hypercall(HVCALL_POST_MESSAGE,
+                                                  aligned_msg, NULL,
+                                                  sizeof(*aligned_msg));
+               else
+                       status = HV_STATUS_INVALID_PARAMETER;
+       } else {
                status = hv_do_hypercall(HVCALL_POST_MESSAGE,
                                aligned_msg, NULL);
+       }
 
        local_irq_restore(flags);
 
@@ -105,6 +122,24 @@ int hv_synic_alloc(void)
                tasklet_init(&hv_cpu->msg_dpc,
                             vmbus_on_msg_dpc, (unsigned long) hv_cpu);
 
+               if (ms_hyperv.paravisor_present && hv_isolation_type_tdx()) {
+                       hv_cpu->post_msg_page = (void *)get_zeroed_page(GFP_ATOMIC);
+                       if (hv_cpu->post_msg_page == NULL) {
+                               pr_err("Unable to allocate post msg page\n");
+                               goto err;
+                       }
+
+                       ret = set_memory_decrypted((unsigned long)hv_cpu->post_msg_page, 1);
+                       if (ret) {
+                               pr_err("Failed to decrypt post msg page: %d\n", ret);
+                               /* Just leak the page, as it's unsafe to free the page. */
+                               hv_cpu->post_msg_page = NULL;
+                               goto err;
+                       }
+
+                       memset(hv_cpu->post_msg_page, 0, PAGE_SIZE);
+               }
+
                /*
                 * Synic message and event pages are allocated by paravisor.
                 * Skip these pages allocation here.
@@ -178,6 +213,17 @@ void hv_synic_free(void)
                        = per_cpu_ptr(hv_context.cpu_context, cpu);
 
                /* It's better to leak the page if the encryption fails. */
+               if (ms_hyperv.paravisor_present && hv_isolation_type_tdx()) {
+                       if (hv_cpu->post_msg_page) {
+                               ret = set_memory_encrypted((unsigned long)
+                                       hv_cpu->post_msg_page, 1);
+                               if (ret) {
+                                       pr_err("Failed to encrypt post msg page: %d\n", ret);
+                                       hv_cpu->post_msg_page = NULL;
+                               }
+                       }
+               }
+
                if (!ms_hyperv.paravisor_present &&
                    (hv_isolation_type_en_snp() || hv_isolation_type_tdx())) {
                        if (hv_cpu->synic_message_page) {
@@ -199,6 +245,7 @@ void hv_synic_free(void)
                        }
                }
 
+               free_page((unsigned long)hv_cpu->post_msg_page);
                free_page((unsigned long)hv_cpu->synic_event_page);
                free_page((unsigned long)hv_cpu->synic_message_page);
        }

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 55f2086..f6b1e71 100644 (file)
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -123,6 +123,17 @@ struct hv_per_cpu_context {
        void *synic_message_page;
        void *synic_event_page;
 
+       /*
+        * The page is only used in hv_post_message() for a TDX VM (with the
+        * paravisor) to post a messages to Hyper-V: when such a VM calls
+        * HVCALL_POST_MESSAGE, it can't use the hyperv_pcpu_input_arg (which
+        * is encrypted in such a VM) as the hypercall input page, because
+        * the input page for HVCALL_POST_MESSAGE must be decrypted in such a
+        * VM, so post_msg_page (which is decrypted in hv_synic_alloc()) is
+        * introduced for this purpose. See hyperv_init() for more comments.
+        */
+       void *post_msg_page;
+
        /*
         * Starting with win8, we can take channel interrupts on any CPU;
         * we will manage the tasklet that handles events messages on a per CPU