linux-kernel - [PATCH v4 07/22] x86/fpu/xstate: Calculate and remember dynamic xstate buffer sizes

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Message-Id: <20210221185637.19281-8-chang.seok.bae@intel.com>
Date:   Sun, 21 Feb 2021 10:56:22 -0800
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     bp@...e.de, luto@...nel.org, tglx@...utronix.de, mingo@...nel.org,
        x86@...nel.org
Cc:     len.brown@...el.com, dave.hansen@...el.com, jing2.liu@...el.com,
        ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org,
        chang.seok.bae@...el.com
Subject: [PATCH v4 07/22] x86/fpu/xstate: Calculate and remember dynamic xstate buffer sizes

The xstate buffer is currently embedded into struct fpu with static size.
To accommodate dynamic user xstates, record the maximum and minimum buffer
sizes.

Rename the size calculation function. It calculates the maximum xstate size
and sanity checks it with CPUID. It also calculates the static embedded
buffer size by excluding the dynamic user states from the maximum size.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
---
Changes from v3:
* Updated the changelog. (Borislav Petkov)
* Updated the code comment. (Borislav Petkov)
* Adjusted the calculation function naming.
* Moved out the new variable addition into a new patch.

Changes from v2:
* Updated the changelog with task->fpu removed. (Borislav Petkov)
* Renamed the in-line size variable.
* Updated some code comments.
---
 arch/x86/kernel/fpu/xstate.c | 52 +++++++++++++++++++++++-------------
 1 file changed, 33 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 16379c368714..b7686f107f3a 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -655,23 +655,31 @@ static void check_xstate_against_struct(int nr)
 }
 
 /*
- * This essentially double-checks what the cpu told us about
- * how large the XSAVE buffer needs to be.  We are recalculating
- * it to be safe.
+ * Calculate the xstate per-task buffer sizes -- maximum and minimum.
+ *
+ * And record the minimum. Also double-check the maximum against what
+ * the cpu told.
+ *
+ * Dynamic user states are stored in this buffer. They account for the
+ * delta between the maximum and the minimum.
  *
  * Dynamic supervisor XSAVE features allocate their own buffers and are
- * not covered by these checks. Only the size of the buffer for task->fpu
- * is checked here.
+ * not covered by these checks.
  */
-static void do_extra_xstate_size_checks(void)
+static void calculate_xstate_sizes(void)
 {
-	int paranoid_xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
+	int paranoid_min_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
+	int paranoid_max_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
 	int i;
 
 	for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) {
+		bool user_dynamic;
+
 		if (!xfeature_enabled(i))
 			continue;
 
+		user_dynamic = (xfeatures_mask_user_dynamic & BIT_ULL(i)) ? true : false;
+
 		check_xstate_against_struct(i);
 		/*
 		 * Supervisor state components can be managed only by
@@ -681,23 +689,32 @@ static void do_extra_xstate_size_checks(void)
 			XSTATE_WARN_ON(xfeature_is_supervisor(i));
 
 		/* Align from the end of the previous feature */
-		if (xfeature_is_aligned(i))
-			paranoid_xstate_size = ALIGN(paranoid_xstate_size, 64);
+		if (xfeature_is_aligned(i)) {
+			paranoid_max_size = ALIGN(paranoid_max_size, 64);
+			if (!user_dynamic)
+				paranoid_min_size = ALIGN(paranoid_min_size, 64);
+		}
 		/*
 		 * The offset of a given state in the non-compacted
 		 * format is given to us in a CPUID leaf.  We check
 		 * them for being ordered (increasing offsets) in
 		 * setup_xstate_features().
 		 */
-		if (!using_compacted_format())
-			paranoid_xstate_size = xfeature_uncompacted_offset(i);
+		if (!using_compacted_format()) {
+			paranoid_max_size = xfeature_uncompacted_offset(i);
+			if (!user_dynamic)
+				paranoid_min_size = xfeature_uncompacted_offset(i);
+		}
 		/*
 		 * The compacted-format offset always depends on where
 		 * the previous state ended.
 		 */
-		paranoid_xstate_size += xfeature_size(i);
+		paranoid_max_size += xfeature_size(i);
+		if (!user_dynamic)
+			paranoid_min_size += xfeature_size(i);
 	}
-	XSTATE_WARN_ON(paranoid_xstate_size != get_xstate_config(XSTATE_MAX_SIZE));
+	XSTATE_WARN_ON(paranoid_max_size != get_xstate_config(XSTATE_MAX_SIZE));
+	set_xstate_config(XSTATE_MIN_SIZE, paranoid_min_size);
 }
 
 
@@ -798,14 +815,11 @@ static int __init init_xstate_size(void)
 	 */
 	set_xstate_config(XSTATE_MAX_SIZE, possible_xstate_size);
 
-	/* Perform an extra check for the maximum size. */
-	do_extra_xstate_size_checks();
-
 	/*
-	 * Set the minimum to be the same as the maximum. The dynamic
-	 * user states are not supported yet.
+	 * Calculate and double-check the maximum size. Calculate and record
+	 * the minimum size.
 	 */
-	set_xstate_config(XSTATE_MIN_SIZE, possible_xstate_size);
+	calculate_xstate_sizes();
 
 	/* Ensure the minimum size fits in the statically-alocated buffer: */
 	if (!is_supported_xstate_size(get_xstate_config(XSTATE_MIN_SIZE)))
-- 
2.17.1