On 1/4/21 11:56 AM, Matthew Wilcox wrote:
On Mon, Jan 04, 2021 at 11:38:38AM -0500, Andrey Grodzovsky wrote:
Hello, I am AMD developer and I am trying to implement support for on the
fly graceful graphic card extraction.
Are you talking about surprise removal (eg card on the other end of
a Thunderbolt connector where there is no possibility for software
locking), or are you talking about an orderly removal (where the user
requests removal and there is time to tear everything down gracefully)?
Surprise removal
One issue I am facing is how to avoid
accesses to physical addresses both in RAM and MMIO from user mode and
kernel after device is gone. For user accesses (mmap) I use the page fault
handler to route all RW accesses to dummy zero page. I would like to do the
same for kernel side mappings both form RAM (kmap) and device IO
(ioremap) but it looks like there is no same mechanism of page fault
handlers for kernel side mappings.
ioremap() is done through the vmalloc space. It would, in theory, be
possible to reprogram the page tables used for vmalloc to point to your
magic page. I don't think we have such a mechanism today, and there are
lots of problems with things like TLB flushes. It's probably going to
be harder than you think.
I'm adding the linux-pci mailing list so you can be helped with the
logistics of device hot-remove.
Thanks, that makes sense as I couldn't find any clear documentation on how to handle
page faults for kernel page table while there is a clear mechanism and
documenting on how
it's done for user processes page tables (implementing the
vm_operations_struct.fault callback)
It indeed the would be useful if some one (maybe on PCI side) could give me an
advise on how
best to avoid accessing MMIO mappings made through ioremap once I identify the
device is gone.
The best we came up with until now is to explicitly test for device being preset
before
doing any MMIO r/w access.
Andrey
