On Thu 2020-01-30 19:39:17, Greg Kroah-Hartman wrote:
From: Fenghua Yu fenghua.yu@intel.com
[ Upstream commit f11421ba4af706cb4f5703de34fa77fba8472776 ]
This is not suitable for stable. It does not fix anything. It prepares for theoretical bug that author claims might be introduced to BIOS in future... I doubt it, even BIOS authors boot their machines from time to time.
Atomic operations that span cache lines are super-expensive on x86 (not just to the current processor, but also to other processes as all memory operations are blocked until the operation completes). Upcoming x86 processors have a switch to cause such operations to generate a #AC trap. It is expected that some real time systems will enable this mode in BIOS.
And I wonder if this is even good idea for mainline. x86 architecture is here for long time, and I doubt Intel is going to break it like this. Do you have documentation pointer?
In preparation for this, it is necessary to fix code that may execute atomic instructions with operands that cross cachelines because the #AC trap will crash the kernel.
How does single bit operation "cross cacheline"? How is this going to impact non-x86 architectures?
Since "pwol_mask" is local and never exposed to concurrency, there is no need to set bits in pwol_mask using atomic operations.
Directly operate on the byte which contains the bit instead of using __set_bit() to avoid any big endian concern due to type cast to unsigned long in __set_bit().
What concerns? Is __set_bit() now useless and are we going to open-code it everywhere? Is set_bit() now unusable on x86? Pavel
Suggested-by: Peter Zijlstra peterz@infradead.org Signed-off-by: Fenghua Yu fenghua.yu@intel.com Signed-off-by: Tony Luck tony.luck@intel.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org
drivers/net/ethernet/broadcom/b44.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/broadcom/b44.c index e445ab724827f..88f8d31e4c833 100644 --- a/drivers/net/ethernet/broadcom/b44.c +++ b/drivers/net/ethernet/broadcom/b44.c @@ -1519,8 +1519,10 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppattern, u8 *pmask, int offset) int ethaddr_bytes = ETH_ALEN; memset(ppattern + offset, 0xff, magicsync);
- for (j = 0; j < magicsync; j++)
set_bit(len++, (unsigned long *) pmask);
- for (j = 0; j < magicsync; j++) {
pmask[len >> 3] |= BIT(len & 7);len++;- }
for (j = 0; j < B44_MAX_PATTERNS; j++) { if ((B44_PATTERN_SIZE - len) >= ETH_ALEN) @@ -1532,7 +1534,8 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppattern, u8 *pmask, int offset) for (k = 0; k< ethaddr_bytes; k++) { ppattern[offset + magicsync + (j * ETH_ALEN) + k] = macaddr[k];
set_bit(len++, (unsigned long *) pmask);
pmask[len >> 3] |= BIT(len & 7);len++;-- 2.20.1