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authorDexuan Cui <decui@microsoft.com>2023-08-24 01:07:09 -0700
committerWei Liu <wei.liu@kernel.org>2023-08-25 00:04:57 +0000
commit23378295042a4bcaeec350733a4771678e7a1f3a (patch)
tree96e4447fe9da4a905966d611f98ace45fb4ea714
parentd3a9d7e49d15316f68f4347f48adcd1665834980 (diff)
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
-rw-r--r--arch/x86/hyperv/hv_init.c20
-rw-r--r--drivers/hv/hv.c59
-rw-r--r--drivers/hv/hyperv_vmbus.h11
3 files changed, 82 insertions, 8 deletions
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index eca5c4b7e3b5..3729eee21e47 100644
--- 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 48b1623112f0..523c5d99f375 100644
--- 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 55f2086841ae..f6b1e710f805 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -124,6 +124,17 @@ struct hv_per_cpu_context {
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
* basis.