A TDX VM on Hyper-V may run in TD mode or Partitioned TD mode (L2). For
the former, the VM has not enabled the Hyper-V TSC page (which is defined
in drivers/clocksource/hyperv_timer.c: "... tsc_pg __bss_decrypted ...")
because, for such a VM, the hypervisor requires that the page should be
shared, but currently the __bss_decrypted is not working for such a VM
yet.
Hyper-V TSC page can work as a clocksource device similar to KVM pv
clock, and it's also used by the Hyper-V timer code to get the current
time: see hv_init_tsc_clocksource(), which sets the global function
pointer hv_read_reference_counter to read_hv_clock_tsc(); when
Hyper-V TSC page is not enabled, hv_read_reference_counter defaults to
be drivers/hv/hv_common.c: __hv_read_ref_counter(), which is suboptimal
as it uses the slow MSR interface to get the time info.
The attribute __bss_decrypted was added for a native SNP VM by the
commit 45f46b1ac95e ("clocksource: hyper-v: Mark hyperv tsc page unencrypted in
sev-snp enlightened guest")
The attribute works for SNP because of the commit below
commit b3f0907c71e0 ("x86/mm: Add .bss..decrypted section to hold shared
variables")
The attribute is not working for TDX because __startup_64() ->
sme_postprocess_startup() is not for TDX; we can't just call
set_memory_decrypted() in sme_postprocess_startup() because
sme_postprocess_startup() runs too early and set_memory_decrypted() is not
working there yet.
This RFC patch calls set_memory_decrypted() in a later place, i.e., in
start_kernel() -> setup_arch() -> init_hypervisor_platform() ->
ms_hyperv_init_platform(), so set_memory_decrypted() works there;
accordingly, mem_encrypt_free_decrypted_mem() -> set_memory_encrypted()
must be called for TDX now.
When a TDX VM runs in Partitioned TD mode (L2), the Hyper-V TSC page should
be a private page, so set_memory_decrypted() should not be called for the
page in such a VM. Introduce a global variable "tdx_partitioned_td_l2" to
handle this type of VM differently.
BTW, the 4KB Hyper-V TSC page is enabled very early in
hv_init_tsc_clocksource(), where set_memory_decrypted() is not working yet,
so we can't simply call set_memory_decrypted() in hv_init_tsc_clocksource()
for a TDX VM in TD mode, and we need to get the attribute __bss_decrypted
to work for such a VM.
The changes to arch/x86/kernel/cpu/mshyperv.c and
arch/x86/mm/mem_encrypt_amd.c are not satisfying to me. I wish there
could be a better way to support __bss_decrypted for a native TDX VM
so that a TDX VM on KVM could also benefit from __bss_decrypted, if
some one wants to use it in future. BTW, kvm_init_platform() has
similar code for SNP.
This is just a RFC patch. I apprecite your insight. Thanks!
Signed-off-by: Dexuan Cui <de...@microsoft.com>
---
arch/x86/coco/core.c | 15 +++++++++++++++
arch/x86/coco/tdx/tdx.c | 2 ++
arch/x86/hyperv/ivm.c | 3 ++-
arch/x86/include/asm/tdx.h | 1 +
arch/x86/kernel/cpu/mshyperv.c | 8 ++++++--
arch/x86/mm/mem_encrypt_amd.c | 3 ++-
6 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index b31ef2424d194..61cec405f1084 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -15,6 +15,7 @@
#include <asm/archrandom.h>
#include <asm/coco.h>
+#include <asm/tdx.h>
#include <asm/processor.h>
enum cc_vendor cc_vendor __ro_after_init = CC_VENDOR_NONE;
@@ -25,8 +26,22 @@ static struct cc_attr_flags {
__resv : 63;
} cc_flags;
+static bool noinstr intel_cc_platform_td_l2(enum cc_attr attr)
+{
+ switch (attr) {
+ case CC_ATTR_GUEST_MEM_ENCRYPT:
+ case CC_ATTR_MEM_ENCRYPT:
+ return true;
+ default:
+ return false;
+ }
+}
+
static bool noinstr intel_cc_platform_has(enum cc_attr attr)
{
+ if (tdx_partitioned_td_l2)
+ return intel_cc_platform_td_l2(attr);
+
switch (attr) {
case CC_ATTR_GUEST_UNROLL_STRING_IO:
case CC_ATTR_HOTPLUG_DISABLED:
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index abf3cd591afd3..8e6ab42add7c0 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -39,6 +39,8 @@
#define TDREPORT_SUBTYPE_0 0
+bool tdx_partitioned_td_l2 __ro_after_init;
+
/* Called from __tdx_hypercall() for unrecoverable failure */
noinstr void __noreturn __tdx_hypercall_failed(void)
{
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 768d73de0d098..52cd44e507846 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -626,7 +626,7 @@ static bool hv_is_private_mmio(u64 addr)
return false;
}
-void __init hv_vtom_init(void)
+void __init hv_vtom_init(void) /* TODO: rename the function for TDX */
{
enum hv_isolation_type type = hv_get_isolation_type();
@@ -650,6 +650,7 @@ void __init hv_vtom_init(void)
case HV_ISOLATION_TYPE_TDX:
cc_vendor = CC_VENDOR_INTEL;
+ tdx_partitioned_td_l2 = true;
break;
default:
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index eba178996d845..ddcc9ef82dc99 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -66,6 +66,7 @@ int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport);
u64 tdx_hcall_get_quote(u8 *buf, size_t size);
+extern bool tdx_partitioned_td_l2;
#else
static inline void tdx_early_init(void) { };
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index e0fd57a8ba840..7c336bc020c9f 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -18,6 +18,7 @@
#include <linux/kexec.h>
#include <linux/i8253.h>
#include <linux/random.h>
+#include <linux/set_memory.h>
#include <asm/processor.h>
#include <asm/hypervisor.h>
#include <asm/hyperv-tlfs.h>
@@ -449,8 +450,11 @@ static void __init ms_hyperv_init_platform(void)
ms_hyperv.hints &= ~HV_X64_APIC_ACCESS_RECOMMENDED;
if (!ms_hyperv.paravisor_present) {
- /* To be supported: more work is required. */
- ms_hyperv.features &=
~HV_MSR_REFERENCE_TSC_AVAILABLE;
+ unsigned long vaddr = (unsigned
long)__start_bss_decrypted;
+ unsigned long vaddr_end = (unsigned
long)__end_bss_decrypted;
+
+ for (; vaddr < vaddr_end; vaddr += PMD_SIZE)
+ set_memory_decrypted(vaddr, PMD_SIZE >>
PAGE_SHIFT);
/* HV_MSR_CRASH_CTL is unsupported. */
ms_hyperv.misc_features &=
~HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE;
diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
index 422602f6039b8..0ddb9e5d222c3 100644
--- a/arch/x86/mm/mem_encrypt_amd.c
+++ b/arch/x86/mm/mem_encrypt_amd.c
@@ -25,6 +25,7 @@
#include <asm/fixmap.h>
#include <asm/setup.h>
#include <asm/mem_encrypt.h>
+#include <asm/tdx.h>
#include <asm/bootparam.h>
#include <asm/set_memory.h>
#include <asm/cacheflush.h>
@@ -529,7 +530,7 @@ void __init mem_encrypt_free_decrypted_mem(void)
* CC_ATTR_MEM_ENCRYPT, aren't necessarily equivalent in a Hyper-V VM
* using vTOM, where sme_me_mask is always zero.
*/
- if (sme_me_mask) {
+ if (sme_me_mask || (cc_vendor == CC_VENDOR_INTEL &&
!tdx_partitioned_td_l2)) {
r = set_memory_encrypted(vaddr, npages);
if (r) {
pr_warn("failed to free unused decrypted pages\n");
--
2.25.1
