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SubjectRe: [Xen-devel] [PATCH] auto balloon initial domain and fix dom0_mem=X inconsistencies (v5).
On 03/05/12 12:48, David Vrabel wrote:
> On 01/05/12 17:37, Konrad Rzeszutek Wilk wrote:
>> On Mon, Apr 16, 2012 at 01:15:31PM -0400, Konrad Rzeszutek Wilk wrote:
>>> Changelog v5 [since v4]:
>>> - used populate_physmap, fixed bugs.
>>> [v2-v4: not posted]
>>> - reworked the code in setup.c to work properly.
>>> [v1: https://lkml.org/lkml/2012/3/30/492]
>>> - initial patchset
>>
>> One bug I found was that with 'dom0_mem=max:1G' (with and without these
>> patches) I would get a bunch of
>>
>> (XEN) page_alloc.c:1148:d0 Over-allocation for domain 0: 2097153 > 2097152
>> (XEN) memory.c:133:d0 Could not allocate order=0 extent: id=0 memflags=0 (0 of 17)
>>
>> where the (0 of X), sometimes was 1, 2,3,4 or 17 -depending on the machine
>> I ran on it. I figured it out that the difference was in the ACPI tables
>> that are allocated - and that those regions - even though are returned
>> back to the hypervisor, cannot be repopulated. I can't find the actual
>> exact piece of code in the hypervisor to pin-point and say "Aha".
>
> It was tricky to track down what is going here but I think I see what's
> happening.
>
> The problem pages (on the system I looked at) were located just before
> the ISA memory region (so PFN < a0) and so they are mapped in the
> bootstrap page tables and have an additional ref so are not immediately
> freed when the page is released. They do get freed later on, presumably
> when the page tables are swapped over.

It's not the bootstrap page tables but those constructed in
xen_setup_kernel_pagetable() but this has the same effect.

> I think the mapping needs to be removed with
> HYPERVISOR_update_va_mapping() before releasing the page. This is
> already done for the ISA region in xen_ident_map_ISA().

And here's a patch that does this. I've not given it a lot of testing.

This is on top of your 8/8 patch and your "xen/setup: Cap amount to
populate based on current tot_pages count." patch is no longer needed.

David

8<---------------------
From 17900ce942ed34ccc85b8e6fbce392118d95d9d3 Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel@citrix.com>
Date: Thu, 3 May 2012 15:57:00 +0100
Subject: [PATCH] xen: update VA mapping when releasing memory during setup
In xen_memory_setup(), if a page that is being released has a VA
mapping this must also be updated. Otherwise, the page will be not
released completely -- it will still be referenced in Xen and won't be
freed util the mapping is removed and this prevents it from being
reallocated at a different PFN.

This was already being done for the ISA memory region in
xen_ident_map_ISA() but on many systems this was omitting a few pages
as many systems marked a few pages below the ISA memory region as
reserved in the e820 map.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
arch/x86/xen/enlighten.c | 1 -
arch/x86/xen/mmu.c | 23 -----------------------
arch/x86/xen/setup.c | 41 ++++++++++++++++++++++++++++++++++-------
arch/x86/xen/xen-ops.h | 1 -
4 files changed, 34 insertions(+), 32 deletions(-)
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index a8f8844..ff9a20a 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1306,7 +1306,6 @@ asmlinkage void __init xen_start_kernel(void)

xen_raw_console_write("mapping kernel into physical memory\n");
pgd = xen_setup_kernel_pagetable(pgd, xen_start_info->nr_pages);
- xen_ident_map_ISA();

/* Allocate and initialize top and mid mfn levels for p2m structure */
xen_build_mfn_list_list();
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index b8e2794..b756d8c 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1929,29 +1929,6 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
#endif
}

-void __init xen_ident_map_ISA(void)
-{
- unsigned long pa;
-
- /*
- * If we're dom0, then linear map the ISA machine addresses into
- * the kernel's address space.
- */
- if (!xen_initial_domain())
- return;
-
- xen_raw_printk("Xen: setup ISA identity maps\n");
-
- for (pa = ISA_START_ADDRESS; pa < ISA_END_ADDRESS; pa += PAGE_SIZE) {
- pte_t pte = mfn_pte(PFN_DOWN(pa), PAGE_KERNEL_IO);
-
- if (HYPERVISOR_update_va_mapping(PAGE_OFFSET + pa, pte, 0))
- BUG();
- }
-
- xen_flush_tlb();
-}
-
static void __init xen_post_allocator_init(void)
{
pv_mmu_ops.set_pte = xen_set_pte;
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 506a3e6..d5f8714 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -139,6 +139,13 @@ static unsigned long __init xen_do_chunk(unsigned long start,

return len;
}
+
+static unsigned long __init xen_release_chunk(unsigned long start,
+ unsigned long end)
+{
+ return xen_do_chunk(start, end, true);
+}
+
static unsigned long __init xen_populate_chunk(
const struct e820entry *list, size_t map_size,
unsigned long max_pfn, unsigned long *last_pfn,
@@ -197,6 +204,29 @@ static unsigned long __init xen_populate_chunk(
}
return done;
}
+
+static void __init xen_set_identity_and_release_chunk(
+ unsigned long start_pfn, unsigned long end_pfn, unsigned long nr_pages,
+ unsigned long *released, unsigned long *identity)
+{
+ unsigned long pfn;
+
+ /*
+ * If the PFNs are currently mapped, the VA mapping also needs
+ * to be updated to be 1:1.
+ */
+ for (pfn = start_pfn; pfn <= max_pfn_mapped && pfn < end_pfn; pfn++)
+ (void)HYPERVISOR_update_va_mapping(
+ (unsigned long)__va(pfn << PAGE_SHIFT),
+ mfn_pte(pfn, PAGE_KERNEL_IO), 0);
+
+ if (start_pfn < nr_pages)
+ *released += xen_release_chunk(
+ start_pfn, min(end_pfn, nr_pages));
+
+ *identity += set_phys_range_identity(start_pfn, end_pfn);
+}
+
static unsigned long __init xen_set_identity_and_release(
const struct e820entry *list, size_t map_size, unsigned long nr_pages)
{
@@ -226,14 +256,11 @@ static unsigned long __init xen_set_identity_and_release(
if (entry->type == E820_RAM)
end_pfn = PFN_UP(entry->addr);

- if (start_pfn < end_pfn) {
- if (start_pfn < nr_pages)
- released += xen_do_chunk(
- start_pfn, min(end_pfn, nr_pages), true);
+ if (start_pfn < end_pfn)
+ xen_set_identity_and_release_chunk(
+ start_pfn, end_pfn, nr_pages,
+ &released, &identity);

- identity += set_phys_range_identity(
- start_pfn, end_pfn);
- }
start = end;
}
}
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index b095739..506fa08 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -28,7 +28,6 @@ void xen_setup_shared_info(void);
void xen_build_mfn_list_list(void);
void xen_setup_machphys_mapping(void);
pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn);
-void xen_ident_map_ISA(void);
void xen_reserve_top(void);
extern unsigned long xen_max_p2m_pfn;

--
1.7.2.5

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