[PATCH v6 4/6] x86/hyperv: Support hypercalls for TDX guests

Dexuan Cui
2023-05-04T22:55:13Z

A TDX guest uses the GHCI call rather than hv_hypercall_pg.

In hv_do_hypercall(), Hyper-V requires that the input/output addresses
must have the cc_mask.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---

Changes in v2:
Implemented hv_tdx_hypercall() in C rather than in assembly code.
Renamed the parameter names of hv_tdx_hypercall().
Used cc_mkdec() directly in hv_do_hypercall().

Changes in v3:
Decrypted/encrypted hyperv_pcpu_input_arg in
hv_common_cpu_init() and hv_common_cpu_die().

Changes in v4:
__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT) -> __tdx_hypercall_ret()
hv_common_cpu_die(): explicitly ignore the error set_memory_encrypted() [Michael Kelley]
Added Sathyanarayanan's Reviewed-by.

Changes in v5:
Added Michael's Reviewed-by.

Changes in v6: None.

arch/x86/hyperv/hv_init.c | 8 ++++++++
arch/x86/hyperv/ivm.c | 14 ++++++++++++++
arch/x86/include/asm/mshyperv.h | 17 +++++++++++++++++
drivers/hv/hv_common.c | 24 ++++++++++++++++++++++++
4 files changed, 63 insertions(+)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index a5f9474f08e1..f175e0de821c 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -432,6 +432,10 @@ 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())
+ goto skip_hypercall_pg_init;
+
hv_hypercall_pg = __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START,
VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_ROX,
VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
@@ -471,6 +475,7 @@ void __init hyperv_init(void)
wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
}

+skip_hypercall_pg_init:
/*
* hyperv_init() is called before LAPIC is initialized: see
* apic_intr_mode_init() -> x86_platform.apic_post_init() and
@@ -594,6 +599,9 @@ bool hv_is_hyperv_initialized(void)
if (x86_hyper_type != X86_HYPER_MS_HYPERV)
return false;

+ /* A TDX guest uses the GHCI call rather than hv_hypercall_pg. */
+ if (hv_isolation_type_tdx())
+ return true;
/*
* Verify that earlier initialization succeeded by checking
* that the hypercall page is setup
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 952117ce2d80..61ff7060b39b 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -415,3 +415,17 @@ bool hv_isolation_type_tdx(void)
{
return static_branch_unlikely(&isolation_type_tdx);
}
+
+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
+{
+ struct tdx_hypercall_args args = { };
+
+ args.r10 = control;
+ args.rdx = param1;
+ args.r8 = param2;
+
+ (void)__tdx_hypercall_ret(&args);
+
+ return args.r11;
+}
+EXPORT_SYMBOL_GPL(hv_tdx_hypercall);
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 231e56631295..945e5afaba69 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -10,6 +10,7 @@
#include <asm/nospec-branch.h>
#include <asm/paravirt.h>
#include <asm/mshyperv.h>
+#include <asm/coco.h>

/*
* Hyper-V always provides a single IO-APIC at this MMIO address.
@@ -54,6 +55,12 @@ int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);

+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
+
+/*
+ * If the hypercall involves no input or output parameters, the hypervisor
+ * ignores the corresponding GPA pointer.
+ */
static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
{
u64 input_address = input ? virt_to_phys(input) : 0;
@@ -61,6 +68,10 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
u64 hv_status;

#ifdef CONFIG_X86_64
+ if (hv_isolation_type_tdx())
+ return hv_tdx_hypercall(control,
+ cc_mkdec(input_address),
+ cc_mkdec(output_address));
if (!hv_hypercall_pg)
return U64_MAX;

@@ -104,6 +115,9 @@ static inline u64 _hv_do_fast_hypercall8(u64 control, u64 input1)
u64 hv_status;

#ifdef CONFIG_X86_64
+ if (hv_isolation_type_tdx())
+ return hv_tdx_hypercall(control, input1, 0);
+
{
__asm__ __volatile__(CALL_NOSPEC
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
@@ -149,6 +163,9 @@ static inline u64 _hv_do_fast_hypercall16(u64 control, u64 input1, u64 input2)
u64 hv_status;

#ifdef CONFIG_X86_64
+ if (hv_isolation_type_tdx())
+ return hv_tdx_hypercall(control, input1, input2);
+
{
__asm__ __volatile__("mov %4, %%r8\n"
CALL_NOSPEC
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index 6156114cd9c5..5b32adff0e61 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -24,6 +24,7 @@
#include <linux/kmsg_dump.h>
#include <linux/slab.h>
#include <linux/dma-map-ops.h>
+#include <linux/set_memory.h>
#include <asm/hyperv-tlfs.h>
#include <asm/mshyperv.h>

@@ -359,6 +360,7 @@ int hv_common_cpu_init(unsigned int cpu)
u64 msr_vp_index;
gfp_t flags;
int pgcount = hv_root_partition ? 2 : 1;
+ int ret;

/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
flags = irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL;
@@ -368,6 +370,17 @@ int hv_common_cpu_init(unsigned int cpu)
if (!(*inputarg))
return -ENOMEM;

+ if (hv_isolation_type_tdx()) {
+ ret = set_memory_decrypted((unsigned long)*inputarg, pgcount);
+ if (ret) {
+ /* It may be unsafe to free *inputarg */
+ *inputarg = NULL;
+ return ret;
+ }
+
+ memset(*inputarg, 0x00, pgcount * HV_HYP_PAGE_SIZE);
+ }
+
if (hv_root_partition) {
outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
*outputarg = (char *)(*inputarg) + HV_HYP_PAGE_SIZE;
@@ -388,6 +401,8 @@ int hv_common_cpu_die(unsigned int cpu)
unsigned long flags;
void **inputarg, **outputarg;
void *mem;
+ int pgcount = hv_root_partition ? 2 : 1;
+ int ret;

local_irq_save(flags);

@@ -402,6 +417,15 @@ int hv_common_cpu_die(unsigned int cpu)

local_irq_restore(flags);

+ if (hv_isolation_type_tdx()) {
+ ret = set_memory_encrypted((unsigned long)mem, pgcount);
+ if (ret)
+ pr_warn("Hyper-V: Failed to encrypt input arg on cpu%d: %d\n",
+ cpu, ret);
+ /* It's unsafe to free 'mem'. */
+ return 0;
+ }
+
kfree(mem);

return 0;
--
2.25.1