On 01.12.20 13:03, Alex Bennée wrote:
Hi Alex
Oleksandr Tyshchenko <olekst...@gmail.com> writes:
From: Oleksandr Tyshchenko <oleksandr_tyshche...@epam.com>
As a lot of x86 code can be re-used on Arm later on, this
patch makes some preparation to x86/hvm/ioreq.c before moving
to the common code. This way we will get a verbatim copy
<snip>
It worth mentioning that a code which checks the return value of
p2m_set_ioreq_server() in hvm_map_mem_type_to_ioreq_server() was
folded into arch_ioreq_server_map_mem_type() for the clear split.
So the p2m_change_entry_type_global() is called with ioreq_server
lock held.
<snip>
+/* Called with ioreq_server lock held */
+int arch_ioreq_server_map_mem_type(struct domain *d,
+ struct hvm_ioreq_server *s,
+ uint32_t flags)
+{
+ int rc = p2m_set_ioreq_server(d, flags, s);
+
+ if ( rc == 0 && flags == 0 )
+ {
+ const struct p2m_domain *p2m = p2m_get_hostp2m(d);
+
+ if ( read_atomic(&p2m->ioreq.entry_count) )
+ p2m_change_entry_type_global(d, p2m_ioreq_server, p2m_ram_rw);
+ }
+
+ return rc;
+}
+
/*
* Map or unmap an ioreq server to specific memory type. For now, only
* HVMMEM_ioreq_server is supported, and in the future new types can be
@@ -1112,19 +1155,11 @@ int hvm_map_mem_type_to_ioreq_server(struct domain *d,
ioservid_t id,
if ( s->emulator != current->domain )
goto out;
- rc = p2m_set_ioreq_server(d, flags, s);
+ rc = arch_ioreq_server_map_mem_type(d, s, flags);
out:
spin_unlock_recursive(&d->arch.hvm.ioreq_server.lock);
- if ( rc == 0 && flags == 0 )
- {
- struct p2m_domain *p2m = p2m_get_hostp2m(d);
-
- if ( read_atomic(&p2m->ioreq.entry_count) )
- p2m_change_entry_type_global(d, p2m_ioreq_server, p2m_ram_rw);
- }
-
It should be noted that p2m holds it's own lock but I'm unfamiliar with
Xen's locking architecture. Is there anything that prevents another vCPU
accessing a page that is also being used my ioreq on the first vCPU?
I am not sure that I would be able to provide reasonable explanations here.
All what I understand is that p2m_change_entry_type_global() x86
specific (we don't have p2m_ioreq_server concept on Arm) and should
remain as such (not exposed to the common code).
IIRC, I raised a question during V2 review whether we could have ioreq
server lock around the call to p2m_change_entry_type_global() and didn't
get objections. I may mistake, but looks like the lock being used
in p2m_change_entry_type_global() is yet another lock for protecting
page table operations, so unlikely we could get into the trouble calling
this function with the ioreq server lock held.
Assuming that deadlock isn't a possibility to my relatively untrained
eye this looks good to me:
Reviewed-by: Alex Bennée <alex.ben...@linaro.org>
Thank you.
--
Regards,
Oleksandr Tyshchenko
