[RFC PATCH 04/13] x86/fpu/xstate: Enumerate User Interrupts supervisor state

[Sohil Mehta]

Enable xstate supervisor support for User Interrupts by default.

The user interrupt state for a task consists of the MSR state and the
User Interrupt Flag (UIF) value. XSAVES and XRSTORS handle saving and
restoring both of these states.

<The supervisor XSTATE code might be reworked based on issues reported
in the past. The Uintr context switching code would also need rework and
additional testing in that regard.>

Signed-off-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
---
 arch/x86/include/asm/fpu/types.h  | 20 +++++++++++++++++++-
 arch/x86/include/asm/fpu/xstate.h |  3 ++-
 arch/x86/kernel/cpu/common.c      |  6 ++++++
 arch/x86/kernel/fpu/xstate.c      | 20 +++++++++++++++++---
 4 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index f5a38a5f3ae1..b614f1416bea 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -118,7 +118,7 @@ enum xfeature {
 	XFEATURE_RSRVD_COMP_11,
 	XFEATURE_RSRVD_COMP_12,
 	XFEATURE_RSRVD_COMP_13,
-	XFEATURE_RSRVD_COMP_14,
+	XFEATURE_UINTR,
 	XFEATURE_LBR,
 
 	XFEATURE_MAX,
@@ -135,6 +135,7 @@ enum xfeature {
 #define XFEATURE_MASK_PT		(1 << XFEATURE_PT_UNIMPLEMENTED_SO_FAR)
 #define XFEATURE_MASK_PKRU		(1 << XFEATURE_PKRU)
 #define XFEATURE_MASK_PASID		(1 << XFEATURE_PASID)
+#define XFEATURE_MASK_UINTR		(1 << XFEATURE_UINTR)
 #define XFEATURE_MASK_LBR		(1 << XFEATURE_LBR)
 
 #define XFEATURE_MASK_FPSSE		(XFEATURE_MASK_FP | XFEATURE_MASK_SSE)
@@ -237,6 +238,23 @@ struct pkru_state {
 	u32				pad;
 } __packed;
 
+/*
+ * State component 14 is supervisor state used for User Interrupts state.
+ * The size of this state is 48 bytes
+ */
+struct uintr_state {
+	u64 handler;
+	u64 stack_adjust;
+	u32 uitt_size;
+	u8  uinv;
+	u8  pad1;
+	u8  pad2;
+	u8  uif_pad3;		/* bit 7 - UIF, bits 6:0 - reserved */
+	u64 upid_addr;
+	u64 uirr;
+	u64 uitt_addr;
+} __packed;
+
 /*
  * State component 15: Architectural LBR configuration state.
  * The size of Arch LBR state depends on the number of LBRs (lbr_depth).
diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 109dfcc75299..4dd4e83c0c9d 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -44,7 +44,8 @@
 	(XFEATURE_MASK_USER_SUPPORTED & ~XFEATURE_MASK_PKRU)
 
 /* All currently supported supervisor features */
-#define XFEATURE_MASK_SUPERVISOR_SUPPORTED (XFEATURE_MASK_PASID)
+#define XFEATURE_MASK_SUPERVISOR_SUPPORTED (XFEATURE_MASK_PASID | \
+					    XFEATURE_MASK_UINTR)
 
 /*
  * A supervisor state component may not always contain valuable information,
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 55fee930b6d1..3a0a3f5cfe0f 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -334,6 +334,12 @@ static __always_inline void setup_uintr(struct cpuinfo_x86 *c)
 	if (!cpu_has(c, X86_FEATURE_UINTR))
 		goto disable_uintr;
 
+	/* Confirm XSAVE support for UINTR is present. */
+	if (!cpu_has_xfeatures(XFEATURE_MASK_UINTR, NULL)) {
+		pr_info_once("x86: User Interrupts (UINTR) not enabled. XSAVE support for UINTR is missing.\n");
+		goto clear_uintr_cap;
+	}
+
 	/*
 	 * User Interrupts currently doesn't support PTI. For processors that
 	 * support User interrupts PTI in auto mode will default to off.  Need
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index c8def1b7f8fb..ab19403effb0 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -38,6 +38,10 @@ static const char *xfeature_names[] =
 	"Processor Trace (unused)"	,
 	"Protection Keys User registers",
 	"PASID state",
+	"unknown xstate feature 11",
+	"unknown xstate feature 12",
+	"unknown xstate feature 13",
+	"User Interrupts registers",
 	"unknown xstate feature"	,
 };
 
@@ -53,6 +57,10 @@ static short xsave_cpuid_features[] __initdata = {
 	X86_FEATURE_INTEL_PT,
 	X86_FEATURE_PKU,
 	X86_FEATURE_ENQCMD,
+	-1,			/* Unknown 11 */
+	-1,			/* Unknown 12 */
+	-1,			/* Unknown 13 */
+	X86_FEATURE_UINTR,
 };
 
 /*
@@ -236,6 +244,7 @@ static void __init print_xstate_features(void)
 	print_xstate_feature(XFEATURE_MASK_Hi16_ZMM);
 	print_xstate_feature(XFEATURE_MASK_PKRU);
 	print_xstate_feature(XFEATURE_MASK_PASID);
+	print_xstate_feature(XFEATURE_MASK_UINTR);
 }
 
 /*
@@ -372,7 +381,8 @@ static void __init print_xstate_offset_size(void)
 	 XFEATURE_MASK_PKRU |			\
 	 XFEATURE_MASK_BNDREGS |		\
 	 XFEATURE_MASK_BNDCSR |			\
-	 XFEATURE_MASK_PASID)
+	 XFEATURE_MASK_PASID |			\
+	 XFEATURE_MASK_UINTR)
 
 /*
  * setup the xstate image representing the init state
@@ -532,6 +542,7 @@ static void check_xstate_against_struct(int nr)
 	XCHECK_SZ(sz, nr, XFEATURE_Hi16_ZMM,  struct avx_512_hi16_state);
 	XCHECK_SZ(sz, nr, XFEATURE_PKRU,      struct pkru_state);
 	XCHECK_SZ(sz, nr, XFEATURE_PASID,     struct ia32_pasid_state);
+	XCHECK_SZ(sz, nr, XFEATURE_UINTR,     struct uintr_state);
 
 	/*
 	 * Make *SURE* to add any feature numbers in below if
@@ -539,9 +550,12 @@ static void check_xstate_against_struct(int nr)
 	 * numbers.
 	 */
 	if ((nr < XFEATURE_YMM) ||
-	    (nr >= XFEATURE_MAX) ||
 	    (nr == XFEATURE_PT_UNIMPLEMENTED_SO_FAR) ||
-	    ((nr >= XFEATURE_RSRVD_COMP_11) && (nr <= XFEATURE_LBR))) {
+	    (nr == XFEATURE_RSRVD_COMP_11) ||
+	    (nr == XFEATURE_RSRVD_COMP_12) ||
+	    (nr == XFEATURE_RSRVD_COMP_13) ||
+	    (nr == XFEATURE_LBR) ||
+	    (nr >= XFEATURE_MAX)) {
 		WARN_ONCE(1, "no structure for xstate: %d\n", nr);
 		XSTATE_WARN_ON(1);
 	}
-- 
2.33.0