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authorAlexander Gordeev <agordeev@linux.ibm.com>2022-07-24 16:02:16 +0300
committerVasily Gorbik <gor@linux.ibm.com>2022-09-14 17:46:01 +0300
commit2f0e8aae26a27fe73d033788f8e92188e7584f41 (patch)
tree07c8abbd98e7b51142126c6c5880eaeea65ccaf9 /arch/s390/boot
parent14a3a2624285d36624966935ec12f228d876c028 (diff)
downloadlinux-2f0e8aae26a27fe73d033788f8e92188e7584f41.tar.xz
s390/mm: rework memcpy_real() to avoid DAT-off mode
Function memcpy_real() is an univeral data mover that does not require DAT mode to be able reading from a physical address. Its advantage is an ability to read from any address, even those for which no kernel virtual mapping exists. Although memcpy_real() is interrupt-safe, there are no handlers that make use of this function. The compiler instrumentation have to be disabled and separate no-DAT stack used to allow execution of the function once DAT mode is disabled. Rework memcpy_real() to overcome these shortcomings. As result, data copying (which is primarily reading out a crashed system memory by a user process) is executed on a regular stack with enabled interrupts. Also, use of memcpy_real_buf swap buffer becomes unnecessary and the swapping is eliminated. The above is achieved by using a fixed virtual address range that spans a single page and remaps that page repeatedly when memcpy_real() is called for a particular physical address. Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390/boot')
-rw-r--r--arch/s390/boot/startup.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index 41b7af7a9365..6e7f01ca53e6 100644
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -17,6 +17,7 @@
unsigned long __bootdata_preserved(__kaslr_offset);
unsigned long __bootdata_preserved(__abs_lowcore);
+unsigned long __bootdata_preserved(__memcpy_real_area);
unsigned long __bootdata(__amode31_base);
unsigned long __bootdata_preserved(VMALLOC_START);
unsigned long __bootdata_preserved(VMALLOC_END);
@@ -182,7 +183,9 @@ static void setup_kernel_memory_layout(void)
/* force vmalloc and modules below kasan shadow */
vmax = min(vmax, KASAN_SHADOW_START);
#endif
- __abs_lowcore = round_down(vmax - ABS_LOWCORE_MAP_SIZE, sizeof(struct lowcore));
+ __memcpy_real_area = round_down(vmax - PAGE_SIZE, PAGE_SIZE);
+ __abs_lowcore = round_down(__memcpy_real_area - ABS_LOWCORE_MAP_SIZE,
+ sizeof(struct lowcore));
MODULES_END = round_down(__abs_lowcore, _SEGMENT_SIZE);
MODULES_VADDR = MODULES_END - MODULES_LEN;
VMALLOC_END = MODULES_VADDR;