Hello,
Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote on Mon, 21 Oct
2019 10:01:05 +0200:
> On Fri, 18 Oct 2019 16:36:43 +0200
> Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote:
>
> > Any write with either dd or flashcp to a device driven by the
> > spear_smi.c driver will pass through the spear_smi_cpy_toio()
> > function. This function will get called for chunks of up to 256 bytes.
> > If the amount of data is smaller, we may have a problem if the data
> > length is not 4-byte aligned. In this situation, the kernel panics
> > during the memcpy:
> >
> > # dd if=/dev/urandom bs=1001 count=1 of=/dev/mtd6
> > spear_smi_cpy_toio [620] dest c9070000, src c7be8800, len 256
> > spear_smi_cpy_toio [620] dest c9070100, src c7be8900, len 256
> > spear_smi_cpy_toio [620] dest c9070200, src c7be8a00, len 256
> > spear_smi_cpy_toio [620] dest c9070300, src c7be8b00, len 233
> > Unhandled fault: external abort on non-linefetch (0x808) at 0xc90703e8
> > [...]
> > PC is at memcpy+0xcc/0x330
>
> Can you find out which instruction is at memcpy+0xcc/0x330? For the
> record, the assembly is here [1].
The full disassembled file is attached, here is the failing part:
7: ldmfd sp!, {r5 - r8}
b8: e8bd01e0 pop {r5, r6, r7, r8}
UNWIND( .fnend ) @ end of second stmfd block
UNWIND( .fnstart )
usave r4, lr @ still in first stmdb block
8: movs r2, r2, lsl #31
bc: e1b02f82 lsls r2, r2, #31
ldr1b r1, r3, ne, abort=21f
c0: 14d13001 ldrbne r3, [r1], #1
ldr1b r1, r4, cs, abort=21f
c4: 24d14001 ldrbcs r4, [r1], #1
ldr1b r1, ip, cs, abort=21f
c8: 24d1c001 ldrbcs ip, [r1], #1
str1b r0, r3, ne, abort=21f
cc: 14c03001 strbne r3, [r0], #1
str1b r0, r4, cs, abort=21f
d0: 24c04001 strbcs r4, [r0], #1
str1b r0, ip, cs, abort=21f
d4: 24c0c001 strbcs ip, [r0], #1
exit r4, pc
d8: e8bd8011 pop {r0, r4, pc}
So the fault is triggered on a strbne instruction.
> >
> > Workaround this issue by using the alternate _memcpy_toio() method
> > which at least does not present the same problem.
> >
> > Fixes: f18dbbb1bfe0 ("mtd: ST SPEAr: Add SMI driver for serial NOR flash")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Suggested-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
>
> I don't remember suggesting that as a final solution. I probably
> suggested to test with _memcpy_toio() to see if using a byte accessor
> was fixing the problem, but it's definitely not the right solution
> (using byte access with a memory barrier for 256 bytes buffers is likely
> to cause a huge perf penalty).
>
> > Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
> > ---
> >
> > Hello,
> >
> > This patch could not be tested with a mainline kernel (only compiled)
> > but was tested with a stable 4.14.x kernel. I have really no idea why
> > memcpy fails in this situation that's why I propose this workaround
> > but I bet there is something deeper not working.
> >
> > Thanks,
> > Miquèl
> >
> > drivers/mtd/devices/spear_smi.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/mtd/devices/spear_smi.c b/drivers/mtd/devices/spear_smi.c
> > index 986f81d2f93e..d888625a3244 100644
> > --- a/drivers/mtd/devices/spear_smi.c
> > +++ b/drivers/mtd/devices/spear_smi.c
> > @@ -614,7 +614,7 @@ static inline int spear_smi_cpy_toio(struct spear_smi *dev, u32 bank,
> > ctrlreg1 = readl(dev->io_base + SMI_CR1);
> > writel((ctrlreg1 | WB_MODE) & ~SW_MODE, dev->io_base + SMI_CR1);
> >
> > - memcpy_toio(dest, src, len);
> > + _memcpy_toio(dest, src, len);
> >
> > writel(ctrlreg1, dev->io_base + SMI_CR1);
> >
>
> [1]https://elixir.bootlin.com/linux/v5.4-rc2/source/arch/arm/lib/memcpy.S
Thanks,
Miquèl
Attachment:
memcpy-disassemble
Description: Binary data
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