selftests/mm: Update va_high_addr_switch.sh to check CPU for la57 flag

In order for the page table level 5 to be in use, the CPU must have the setting enabled in addition to the CONFIG option. Check for the flag to be set to avoid false test failures on systems that do not have this cpu flag set.

tools/testing/selftests/mm/va_high_addr_switch.sh +6 -0

@@ -29,9 +29,15 @@ check_supported_x86_64()
 	# See man 1 gzip under '-f'.
 	local pg_table_levels=$(gzip -dcfq "${config}" | grep PGTABLE_LEVELS | cut -d'=' -f 2)
 
+	local cpu_supports_pl5=$(awk '/^flags/ {if (/la57/) {print 0;}
+		else {print 1}; exit}' /proc/cpuinfo 2>/dev/null)
+
 	if [[ "${pg_table_levels}" -lt 5 ]]; then
 		echo "$0: PGTABLE_LEVELS=${pg_table_levels}, must be >= 5 to run this test"
 		exit $ksft_skip
+	elif [[ "${cpu_supports_pl5}" -ne 0 ]]; then
+		echo "$0: CPU does not have the necessary la57 flag to support page table level 5"
+		exit $ksft_skip
 	fi
 }
 

Signature · 1 line

2.43.0

Quoted 5 lines · On Fri, 19 Jan 2024 15:58:01 -0500 Audra Mitchell <[email protected]> wrote:

In order for the page table level 5 to be in use, the CPU must have the setting enabled in addition to the CONFIG option. Check for the flag to be set to avoid false test failures on systems that do not have this cpu flag set.

Thanks.

I'll add

Cc Adam Sindelar <[email protected]>

Fixes 4f2930c6718a ("selftests/vm: only run 128TBswitch with 5-level paging")

Cc <[email protected]>

A more complete description of these "test failures" would be helpful please.

Quoted 20 lines

tools/testing/selftests/mm/va_high_addr_switch.sh +6 -0

@@ -29,9 +29,15 @@ check_supported_x86_64()
 	# See man 1 gzip under '-f'.
 	local pg_table_levels=$(gzip -dcfq "${config}" | grep PGTABLE_LEVELS | cut -d'=' -f 2)
 
+	local cpu_supports_pl5=$(awk '/^flags/ {if (/la57/) {print 0;}
+		else {print 1}; exit}' /proc/cpuinfo 2>/dev/null)
+
 	if [[ "${pg_table_levels}" -lt 5 ]]; then
 		echo "$0: PGTABLE_LEVELS=${pg_table_levels}, must be >= 5 to run this test"
 		exit $ksft_skip
+	elif [[ "${cpu_supports_pl5}" -ne 0 ]]; then
+		echo "$0: CPU does not have the necessary la57 flag to support page table level 5"
+		exit $ksft_skip
 	fi
 }
 

Signature · 1 line

2.43.0

Quoted 3 lines

A more complete description of these "test failures" would be helpful please.

Hey, sorry for the incomplete description. The test does a series of mmap calls including three using the MAP_FIXED flag and specifying an address that is 1<<47 or 1<<48. These addresses are only available if you are using level 5 page tables, which requires both the CPU to have the capabiltiy (la57 flag) and the kernel to be configured. Currently the test only checks for the kernel configuration option, so this test can still report a false positive. Here are the three failing lines:

$ ./va_high_addr_switch | grep FAILED
mmap(ADDR_SWITCH_HINT, 2 * PAGE_SIZE, MAP_FIXED): 0xffffffffffffffff - FAILED
mmap(HIGH_ADDR, MAP_FIXED): 0xffffffffffffffff - FAILED
mmap(ADDR_SWITCH_HINT, 2 * PAGE_SIZE, MAP_FIXED): 0xffffffffffffffff - FAILED

I thought (for about a second) refactoring the test so that these three mmap calls will only be run on systems with the level 5 page tables available, but the whole point of the test is to check the level 5 feature...

If you would like me to also update the description on the patch let me know and I'll update it and resubmit. Thanks!