Peter Xu <pet...@redhat.com> wrote:
> When a ramblock is backed by hugetlbfs and the user specified using
> double-map feature, we trap the faults on these regions using minor mode.
> Teach QEMU about that.
>
> Add some sanity check on the fault flags when receiving a uffd message.
> For minor fault trapped ranges, we should always see the MINOR flag set,
> while when using generic missing faults we should never see it.
>
> Signed-off-by: Peter Xu <pet...@redhat.com>
Reviewed-by: Juan Quintela <quint...@redhat.com>
> - if (!(reg_struct.ioctls & ((__u64)1 << _UFFDIO_COPY))) {
Does qemu have a macro to do this bitmap handling?
> {
> MigrationIncomingState *mis = opaque;
> struct uffd_msg msg;
> + uint64_t address;
> int ret;
> size_t index;
> RAMBlock *rb = NULL;
> @@ -945,6 +980,7 @@ static void *postcopy_ram_fault_thread(void *opaque)
> }
>
> while (true) {
> + bool use_minor_fault, minor_flag;
I think that something on the lines of:
bool src_minor_fault, dst_minor_fault;
will make things simpler. Reviewing, I have to go back to definition
place to know which is which.
> ram_addr_t rb_offset;
> int poll_result;
>
> @@ -1022,22 +1058,37 @@ static void *postcopy_ram_fault_thread(void *opaque)
> break;
> }
>
> - rb_offset = ROUND_DOWN(rb_offset, migration_ram_pagesize(rb));
> -
> trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address,
> - qemu_ram_get_idstr(rb),
> - rb_offset,
> - msg.arg.pagefault.feat.ptid);
> - mark_postcopy_blocktime_begin(
> - (uintptr_t)(msg.arg.pagefault.address),
> - msg.arg.pagefault.feat.ptid, rb);
> + address = ROUND_DOWN(msg.arg.pagefault.address,
> + migration_ram_pagesize(rb));
> + use_minor_fault = postcopy_use_minor_fault(rb);
> + minor_flag = !!(msg.arg.pagefault.flags &
> + UFFD_PAGEFAULT_FLAG_MINOR);
>
> + /*
> + * Do sanity check on the message flags to make sure this is
> + * the one we expect to receive. When using minor fault on
> + * this ramblock, it should _always_ be set; when not using
> + * minor fault, it should _never_ be set.
> + */
> + if (use_minor_fault ^ minor_flag) {
> + error_report("%s: Unexpected page fault flags (0x%"PRIx64") "
> + "for address 0x%"PRIx64" (mode=%s)", __func__,
> + (uint64_t)msg.arg.pagefault.flags,
> + (uint64_t)msg.arg.pagefault.address,
> + use_minor_fault ? "MINOR" : "MISSING");
> + }
> +
> + trace_postcopy_ram_fault_thread_request(
> + address, qemu_ram_get_idstr(rb), rb_offset,
> + msg.arg.pagefault.feat.ptid);
> + mark_postcopy_blocktime_begin(
> + (uintptr_t)(address), msg.arg.pagefault.feat.ptid, rb);
> retry:
> /*
> * Send the request to the source - we want to request one
> * of our host page sizes (which is >= TPS)
> */
> - ret = postcopy_request_page(mis, rb, rb_offset,
> - msg.arg.pagefault.address);
> + ret = postcopy_request_page(mis, rb, rb_offset, address);
This is the only change that I find 'problematic'.
On old code, rb_offset has been ROUND_DOWN, on new code it is not.
On old code we pass msg.arg.pagefault.address, now we use
ROUND_DOW(msg.arg.pagefault.address, mighration_ram_pagesize(rb)).
> if (ret) {
> /* May be network failure, try to wait for recovery */
> postcopy_pause_fault_thread(mis);
> @@ -1694,3 +1745,13 @@ void *postcopy_preempt_thread(void *opaque)
>
> return NULL;
> }
> +
> +/*
> + * Whether we should use MINOR fault to trap page faults? It will be used
> + * when doublemap is enabled on hugetlbfs. The default value will be
> + * false, which means we'll keep using the legacy MISSING faults.
> + */
> +bool postcopy_use_minor_fault(RAMBlock *rb)
> +{
> + return migrate_hugetlb_doublemap() && qemu_ram_is_hugetlb(rb);
> +}
Are you planing using this function outside postocpy-ram.c? Otherwise
if you move up its definition you can make it static and drop the header
change.
Later, Juan.
