Re: [PATCH] tracing/user_events: align uaddr on unsigned long alignment
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2023-09-14 17:16:44
Also in:
lkml
On Thu, 14 Sep 2023 15:11:02 +0200 Clément Léger [off-list ref] wrote:
quoted hunk ↗ jump to hunk
@@ -511,13 +511,19 @@ static int user_event_enabler_write(struct user_event_mm *mm, } kaddr = kmap_local_page(page); + + bit_offset = uaddr & (sizeof(unsigned long) - 1); + if (bit_offset) { + bit_offset *= 8; + uaddr &= ~(sizeof(unsigned long) - 1); + } ptr = kaddr + (uaddr & ~PAGE_MASK); /* Update bit atomically, user tracers must be atomic as well */ if (enabler->event && enabler->event->status) - set_bit(ENABLE_BIT(enabler), ptr); + set_bit(ENABLE_BIT(enabler) + bit_offset, ptr); else - clear_bit(ENABLE_BIT(enabler), ptr); + clear_bit(ENABLE_BIT(enabler) + bit_offset, ptr); kunmap_local(kaddr); unpin_user_pages_dirty_lock(&page, 1, true);
Does this work for big endian machines too?
Little endian layout:
uaddr = 0xbeef0004
enabler = 1;
memory at 0xbeef0000: 00 00 00 00 02 00 00 00
^
addr: 0xbeef0004
(enabler is set )
bitoffset = uaddr & (sizeof(unsigned long) - 1); bitoffset = 4
bit_offset *= 8; bitoffset = 32
uaddr &= ~(sizeof(unsigned long) - 1); uaddr = 0xbeef0000
ptr = kaddr + (uaddr & ~PAGE_MASK);
clear_bit(1 + 32, ptr);
memory at 0xbeef0000: 00 00 00 00 02 00 00 00
^
bit 33 of 0xbeef0000
Now lets look at big endian layout:
uaddr = 0xbeef0004
enabler = 1;
memory at 0xbeef0000: 00 00 00 00 00 00 00 02
^
addr: 0xbeef0004
(enabler is set )
bitoffset = uaddr & (sizeof(unsigned long) - 1); bitoffset = 4
bit_offset *= 8; bitoffset = 32
uaddr &= ~(sizeof(unsigned long) - 1); uaddr = 0xbeef0000
ptr = kaddr + (uaddr & ~PAGE_MASK);
clear_bit(1 + 32, ptr);
memory at 0xbeef0000: 00 00 00 00 00 00 00 02
^
bit 33 of 0xbeef0000
I don't think that's what you expected!
-- Steve