Re: [PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT
From: Oleksandr
Date: Fri Nov 19 2021 - 13:25:21 EST
On 19.11.21 02:32, Stefano Stabellini wrote:
Hi Stefano
On Thu, 11 Nov 2021, Oleksandr wrote:
On 28.10.21 04:28, Stefano Stabellini wrote:
Hi Stefano
I am sorry for the late response.
On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Read the start address of the grant table space from DT
(region 0).
This patch mostly restores behaviour before commit 3cf4095d7446
("arm/xen: Use xen_xlate_map_ballooned_pages to setup grant table")
but trying not to break the ACPI support added after that commit.
So the patch touches DT part only and leaves the ACPI part with
xen_xlate_map_ballooned_pages().
This is a preparation for using Xen extended region feature
where unused regions of guest physical address space (provided
by the hypervisor) will be used to create grant/foreign/whatever
mappings instead of wasting real RAM pages from the domain memory
for establishing these mappings.
The immediate benefit of this change:
- Avoid superpage shattering in Xen P2M when establishing
stage-2 mapping (GFN <-> MFN) for the grant table space
- Avoid wasting real RAM pages (reducing the amount of memory
usuable) for mapping grant table space
- The grant table space is always mapped at the exact
same place (region 0 is reserved for the grant table)
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
Changes RFC -> V2:
- new patch
---
arch/arm/xen/enlighten.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 7f1c106b..dea46ec 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -59,6 +59,9 @@ unsigned long xen_released_pages;
struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS]
__initdata;
static __read_mostly unsigned int xen_events_irq;
+static phys_addr_t xen_grant_frames;
__read_mostly
ok
+#define GRANT_TABLE_INDEX 0
uint32_t xen_start_flags;
EXPORT_SYMBOL(xen_start_flags);
@@ -303,6 +306,7 @@ static void __init xen_acpi_guest_init(void)
static void __init xen_dt_guest_init(void)
{
struct device_node *xen_node;
+ struct resource res;
xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
if (!xen_node) {
@@ -310,6 +314,12 @@ static void __init xen_dt_guest_init(void)
return;
}
+ if (of_address_to_resource(xen_node, GRANT_TABLE_INDEX, &res)) {
+ pr_err("Xen grant table region is not found\n");
+ return;
+ }
+ xen_grant_frames = res.start;
+
xen_events_irq = irq_of_parse_and_map(xen_node, 0);
}
@@ -317,16 +327,20 @@ static int __init xen_guest_init(void)
{
struct xen_add_to_physmap xatp;
struct shared_info *shared_info_page = NULL;
- int cpu;
+ int rc, cpu;
if (!xen_domain())
return 0;
if (!acpi_disabled)
xen_acpi_guest_init();
- else
+ else {
xen_dt_guest_init();
+ if (!xen_grant_frames)
+ return -ENODEV;
maybe we can avoid this, see below
+ }
+
if (!xen_events_irq) {
pr_err("Xen event channel interrupt not found\n");
return -ENODEV;
@@ -370,12 +384,16 @@ static int __init xen_guest_init(void)
for_each_possible_cpu(cpu)
per_cpu(xen_vcpu_id, cpu) = cpu;
- xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
- if (xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
- &xen_auto_xlat_grant_frames.vaddr,
- xen_auto_xlat_grant_frames.count)) {
+ if (!acpi_disabled) {
To make the code more resilient couldn't we do:
if (!acpi_disabled || !xen_grant_frames) {
I think, we can.
On the one hand, indeed the code more resilient and less change.
From the other hand if grant table region is not found then something weird
happened as region 0 is always present in reg property if hypervisor node is
exposed to the guest.
The behavior before commit 3cf4095d7446 ("arm/xen: Use
xen_xlate_map_ballooned_pages to setup grant table") was exactly the same in
the context of the failure if region wasn't found.
...
Well, if we want to make code more resilient, I will update. But, looks like
we also need to switch actions in xen_dt_guest_init() in order to process
xen_events_irq before xen_grant_frames, otherwise we may return after failing
with region and end up not initializing xen_events_irq so xen_guest_init()
will fail earlier than reaches that check.
What do you think?
Yes, you are right. I was re-reading the patch to refresh my memory and
I noticed immediately that xen_dt_guest_init also need to be changed so
that xen_events_irq is set before xen_grant_frames.
I think it is a minor change that doesn't add complexity but make the
code more robust so I think it is a good idea
Great, thank you. Will do in next version.
+ xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
+ rc =
xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
+
&xen_auto_xlat_grant_frames.vaddr,
+
xen_auto_xlat_grant_frames.count);
+ } else
+ rc = gnttab_setup_auto_xlat_frames(xen_grant_frames);
+ if (rc) {
free_percpu(xen_vcpu_info);
- return -ENOMEM;
+ return rc;
}
gnttab_init();
--
Regards,
Oleksandr Tyshchenko