From: =?UTF-8?q?Jan=20H=C3=B6ppner?= <hoeppner@linux.ibm.com>
Date: Mon, 14 Sep 2020 13:56:47 +0200
Subject: s390/dasd: Fix zero write for FBA devices
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Git-commit: 709192d531e5b0a91f20aa14abfe2fc27ddd47af
Patch-mainline: v5.9-rc7
References: bsc#1177808 LTC#188739

A discard request that writes zeros using the global kernel internal
ZERO_PAGE will fail for machines with more than 2GB of memory due to the
location of the ZERO_PAGE.

Fix this by using a driver owned global zero page allocated with GFP_DMA
flag set.

Fixes: 28b841b3a7cb ("s390/dasd: Add discard support for FBA devices")
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Cc: <stable@vger.kernel.org> # 4.14+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/s390/block/dasd_fba.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/s390/block/dasd_fba.c
+++ b/drivers/s390/block/dasd_fba.c
@@ -39,6 +39,7 @@
 MODULE_LICENSE("GPL");
 
 static struct dasd_discipline dasd_fba_discipline;
+static void *dasd_fba_zero_page;
 
 struct dasd_fba_private {
 	struct dasd_fba_characteristics rdc_data;
@@ -269,7 +270,7 @@ static void ccw_write_zero(struct ccw1 *
 	ccw->cmd_code = DASD_FBA_CCW_WRITE;
 	ccw->flags |= CCW_FLAG_SLI;
 	ccw->count = count;
-	ccw->cda = (__u32) (addr_t) page_to_phys(ZERO_PAGE(0));
+	ccw->cda = (__u32) (addr_t) dasd_fba_zero_page;
 }
 
 /*
@@ -810,6 +811,11 @@ dasd_fba_init(void)
 	int ret;
 
 	ASCEBC(dasd_fba_discipline.ebcname, 4);
+
+	dasd_fba_zero_page = (void *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
+	if (!dasd_fba_zero_page)
+		return -ENOMEM;
+
 	ret = ccw_driver_register(&dasd_fba_driver);
 	if (!ret)
 		wait_for_device_probe();
@@ -821,6 +827,7 @@ static void __exit
 dasd_fba_cleanup(void)
 {
 	ccw_driver_unregister(&dasd_fba_driver);
+	free_page((unsigned long)dasd_fba_zero_page);
 }
 
 module_init(dasd_fba_init);