[PATCH v4 2/2] target/i386: add control bits support for LAM

[Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>]

LAM uses CR3[61] and CR3[62] to configure/enable LAM on user pointers.
LAM uses CR4[28] to configure/enable LAM on supervisor pointers.

For CR3 LAM bits, no additional handling needed:
- TCG
  LAM is not supported for TCG of target-i386.  helper_write_crN() and
  helper_vmrun() check max physical address bits before calling
  cpu_x86_update_cr3(), no change needed, i.e. CR3 LAM bits are not allowed
  to be set in TCG.
- gdbstub
  x86_cpu_gdb_write_register() will call cpu_x86_update_cr3() to update cr3.
  Allow gdb to set the LAM bit(s) to CR3, if vcpu doesn't support LAM,
  KVM_SET_SREGS will fail as other reserved bits.

For CR4 LAM bit, its reservation depends on vcpu supporting LAM feature or
not.
- TCG
  LAM is not supported for TCG of target-i386.  helper_write_crN() and
  helper_vmrun() check CR4 reserved bit before calling cpu_x86_update_cr4(),
  i.e. CR4 LAM bit is not allowed to be set in TCG.
- gdbstub
  x86_cpu_gdb_write_register() will call cpu_x86_update_cr4() to update cr4.
  Mask out LAM bit on CR4 if vcpu doesn't support LAM.
- x86_cpu_reset_hold() doesn't need special handling.

Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Tested-by: Xuelian Guo <xuelian.guo@xxxxxxxxx>
---
 target/i386/cpu.h    | 7 ++++++-
 target/i386/helper.c | 4 ++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 18ea755644..598a3fa140 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -261,6 +261,7 @@ typedef enum X86Seg {
 #define CR4_SMAP_MASK   (1U << 21)
 #define CR4_PKE_MASK   (1U << 22)
 #define CR4_PKS_MASK   (1U << 24)
+#define CR4_LAM_SUP_MASK (1U << 28)
 
 #define CR4_RESERVED_MASK \
 (~(target_ulong)(CR4_VME_MASK | CR4_PVI_MASK | CR4_TSD_MASK \
@@ -269,7 +270,8 @@ typedef enum X86Seg {
                 | CR4_OSFXSR_MASK | CR4_OSXMMEXCPT_MASK | CR4_UMIP_MASK \
                 | CR4_LA57_MASK \
                 | CR4_FSGSBASE_MASK | CR4_PCIDE_MASK | CR4_OSXSAVE_MASK \
-                | CR4_SMEP_MASK | CR4_SMAP_MASK | CR4_PKE_MASK | CR4_PKS_MASK))
+                | CR4_SMEP_MASK | CR4_SMAP_MASK | CR4_PKE_MASK | CR4_PKS_MASK \
+                | CR4_LAM_SUP_MASK))
 
 #define DR6_BD          (1 << 13)
 #define DR6_BS          (1 << 14)
@@ -2522,6 +2524,9 @@ static inline uint64_t cr4_reserved_bits(CPUX86State *env)
     if (!(env->features[FEAT_7_0_ECX] & CPUID_7_0_ECX_PKS)) {
         reserved_bits |= CR4_PKS_MASK;
     }
+    if (!(env->features[FEAT_7_1_EAX] & CPUID_7_1_EAX_LAM)) {
+        reserved_bits |= CR4_LAM_SUP_MASK;
+    }
     return reserved_bits;
 }
 
diff --git a/target/i386/helper.c b/target/i386/helper.c
index 2070dd0dda..1da7a7d315 100644
--- a/target/i386/helper.c
+++ b/target/i386/helper.c
@@ -219,6 +219,10 @@ void cpu_x86_update_cr4(CPUX86State *env, uint32_t new_cr4)
         new_cr4 &= ~CR4_PKS_MASK;
     }
 
+    if (!(env->features[FEAT_7_1_EAX] & CPUID_7_1_EAX_LAM)) {
+        new_cr4 &= ~CR4_LAM_SUP_MASK;
+    }
+
     env->cr[4] = new_cr4;
     env->hflags = hflags;
 
-- 
2.25.1