[dpdk-dev] [PATCH] mem: fix alignment of requested virtual areas

[Anatoly Burakov <anatoly.burakov@intel.com>]

The original code did not align any addresses that were requested as
page-aligned, but were different because addr_is_hint was set.

Below fix by Dariusz has introduced an issue where all unaligned addresses
were left as unaligned.

This patch is a partial revert of
commit 7fa7216ed48d ("mem: fix alignment of requested virtual areas")

and implements a proper fix for this issue, by asking for alignment in all
but the following two cases:

1) page size is equal to system page size, or
2) we got an aligned requested address, and will not accept a different one

This ensures that alignment is performed in all cases, except for those we
can guarantee that the address will not need alignment.

Fixes: b7cc54187ea4 ("mem: move virtual area function in common directory")
Fixes: 7fa7216ed48d ("mem: fix alignment of requested virtual areas")
Cc: dariuszx.stojaczyk@intel.com
Cc: stable@dpdk.org

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
---
 lib/librte_eal/common/eal_common_memory.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_memory.c b/lib/librte_eal/common/eal_common_memory.c
index 659cc08f6..fbfb1b055 100644
--- a/lib/librte_eal/common/eal_common_memory.c
+++ b/lib/librte_eal/common/eal_common_memory.c
@@ -66,14 +66,17 @@ eal_get_virtual_area(void *requested_addr, size_t *size,
 		addr_is_hint = true;
 	}
 
-	/* if requested address is not aligned by page size, or if requested
-	 * address is NULL, add page size to requested length as we may get an
-	 * address that's aligned by system page size, which can be smaller than
-	 * our requested page size. additionally, we shouldn't try to align if
-	 * system page size is the same as requested page size.
+	/* we don't need alignment of resulting pointer in the following cases:
+	 *
+	 * 1. page size is equal to system size
+	 * 2. we have a requested address, and it is page-aligned, and we will
+	 *    be discarding the address if we get a different one.
+	 *
+	 * for all other cases, alignment is potentially necessary.
 	 */
 	no_align = (requested_addr != NULL &&
-		((uintptr_t)requested_addr & (page_sz - 1))) ||
+		requested_addr == RTE_PTR_ALIGN(requested_addr, page_sz) &&
+		!addr_is_hint) ||
 		page_sz == system_page_sz;
 
 	do {
-- 
2.17.1