s390/sthyi: Use cached data when diag is busy

When sthyi is being emulated, data from diag204 is used. If diag204
returns busy, previously cached sthyi info block is returned to the
caller and cache expiry is set to expired.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Tobias Huschle <huschle@linux.ibm.com>
Signed-off-by: Tobias Huschle <huschle@linux.ibm.com>
Signed-off-by: Mete Durlu <meted@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: NickJackolson

arch/s390/kernel/sthyi.c

@@ -300,7 +300,7 @@ static struct diag204_x_part_block *lpar_cpu_inf(struct lpar_cpu_inf *part_inf,
 	return (struct diag204_x_part_block *)&block->cpus[i];
 }
 
-static void *diag204_get_data(void)
+static void *diag204_get_data(bool diag204_allow_busy)
 {
 	unsigned long subcode;
 	void *diag204_buf;
@@ -320,6 +320,8 @@ static void *diag204_get_data(void)
 		return ERR_PTR(-ENOMEM);
 	subcode = DIAG204_SUBC_STIB7;
 	subcode |= DIAG204_INFO_EXT;
+	if (diag204_has_bif() && diag204_allow_busy)
+		subcode |= DIAG204_BIF_BIT;
 	rc = diag204(subcode, pages, diag204_buf);
 	if (rc < 0) {
 		vfree(diag204_buf);
@@ -328,22 +330,27 @@ static void *diag204_get_data(void)
 	return diag204_buf;
 }
 
-static void fill_diag(struct sthyi_sctns *sctns)
+static bool is_diag204_cached(struct sthyi_sctns *sctns)
+{
+	/*
+	 * Check if validity bits are set when diag204 data
+	 * is gathered.
+	 */
+	if (sctns->par.infpval1)
+		return true;
+	return false;
+}
+
+static void fill_diag(struct sthyi_sctns *sctns, void *diag204_buf)
 {
 	int i;
 	bool this_lpar;
-	void *diag204_buf;
 	void *diag224_buf = NULL;
 	struct diag204_x_info_blk_hdr *ti_hdr;
 	struct diag204_x_part_block *part_block;
 	struct diag204_x_phys_block *phys_block;
 	struct lpar_cpu_inf lpar_inf = {};
 
-	/* Errors are handled through the validity bits in the response. */
-	diag204_buf = diag204_get_data();
-	if (IS_ERR(diag204_buf))
-		return;
-
 	diag224_buf = (void *)__get_free_page(GFP_KERNEL | GFP_DMA);
 	if (!diag224_buf || diag224(diag224_buf))
 		goto out;
@@ -408,7 +415,6 @@ static void fill_diag(struct sthyi_sctns *sctns)
 
 out:
 	free_page((unsigned long)diag224_buf);
-	vfree(diag204_buf);
 }
 
 static int sthyi(u64 vaddr, u64 *rc)
@@ -430,19 +436,31 @@ static int sthyi(u64 vaddr, u64 *rc)
 
 static int fill_dst(void *dst, u64 *rc)
 {
+	void *diag204_buf;
+
 	struct sthyi_sctns *sctns = (struct sthyi_sctns *)dst;
 
 	/*
 	 * If the facility is on, we don't want to emulate the instruction.
 	 * We ask the hypervisor to provide the data.
 	 */
-	if (test_facility(74))
+	if (test_facility(74)) {
+		memset(dst, 0, PAGE_SIZE);
 		return sthyi((u64)dst, rc);
-
+	}
+	/*
+	 * When emulating, if diag204 returns BUSY don't reset dst buffer
+	 * and use cached data.
+	 */
+	*rc = 0;
+	diag204_buf = diag204_get_data(is_diag204_cached(sctns));
+	if (IS_ERR(diag204_buf))
+		return PTR_ERR(diag204_buf);
+	memset(dst, 0, PAGE_SIZE);
 	fill_hdr(sctns);
 	fill_stsi(sctns);
-	fill_diag(sctns);
-	*rc = 0;
+	fill_diag(sctns, diag204_buf);
+	vfree(diag204_buf);
 	return 0;
 }
 
@@ -461,11 +479,14 @@ static int sthyi_update_cache(u64 *rc)
 {
 	int r;
 
-	memset(sthyi_cache.info, 0, PAGE_SIZE);
 	r = fill_dst(sthyi_cache.info, rc);
-	if (r)
-		return r;
-	sthyi_cache.end = jiffies + CACHE_VALID_JIFFIES;
+	if (r == 0) {
+		sthyi_cache.end = jiffies + CACHE_VALID_JIFFIES;
+	} else if (r == -EBUSY) {
+		/* mark as expired and return 0 to keep using cached data */
+		sthyi_cache.end = jiffies - 1;
+		r = 0;
+	}
 	return r;
 }