On 15/11/13 00:22, Christoffer Dall wrote:
> On Thu, Nov 14, 2013 at 02:37:43PM -0500, Santosh Shilimkar wrote:
>> Slab allocator can allocate memory beyond the lowmem watermark
>> which can lead to false failure of virt_addr_valid().
>>
>> So drop the check. The issue was seen with percpu_alloc()
>> in KVM code which was allocating memory beyond lowmem watermark.
>>
>> Am not completly sure whether this is the right fix and if it could
>> impact any other user of virt_addr_valid(). Without this fix as
>> pointed out the KVM init was failing in my testing.
>>
>> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
>> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
>> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>> Cc: Will Deacon <will.deacon@xxxxxxx>
>>
>> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
>> ---
>> arch/arm/include/asm/memory.h | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
>> index 4dd2145..412da47 100644
>> --- a/arch/arm/include/asm/memory.h
>> +++ b/arch/arm/include/asm/memory.h
>> @@ -343,8 +343,7 @@ static inline __deprecated void *bus_to_virt(unsigned long x)
>> #define ARCH_PFN_OFFSET PHYS_PFN_OFFSET
>>
>> #define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
>> -#define virt_addr_valid(kaddr) ((unsigned long)(kaddr) >= PAGE_OFFSET && (unsigned long)(kaddr) < (unsigned long)high_memory)
>> -
>> +#define virt_addr_valid(kaddr) ((unsigned long)(kaddr) >= PAGE_OFFSET)
>> #endif
>>
>> #include <asm-generic/memory_model.h>
>> --
>> 1.7.9.5
>>
>
> This looks wrong to me. Check Documentation/arm/memory.txt, this would
> return true for the VMALLOC region, which would cause virt_to_phys to
> give you something invalid, which would be bad.
>
> We use the check in create_hyp_mappings to be sure that the physical
> address returned by virt_to_phys is valid and that if we're mapping more
> than one page that those pages are physically contiguous.
>
> So if you want to get rid of this check, you need to change the mapping
> functionality to obtain the physical address by walking the page table
> mappings for each page that you are mapping instead. Or limit each call
> to a single page in size and take the physical address as input and use
> per_cpu_ptr_to_phys at the caller side instead.
>
> Alternatively, we need to get rid of alloc_percpu and use regular
> kmallocs instead, unless anyone else knows of an even better way.
alloc_percpu has nice properties (cache locality, mostly).
One way out of it would be to give percpu stuff a special treatment. Can
you try the attach patch as a first approximation? It needs more
refinements (allocations straddling two pages?), but I think that's the
right sort of things.
Let me know how it works for you.
M.
--
Jazz is not dead. It just smells funny...
>From 01bc1c8eaebdd70b1ea044050144b9bfb3375f82 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <marc.zyngier@xxxxxxx>
Date: Fri, 15 Nov 2013 11:36:36 +0000
Subject: [PATCH] arm/arm64: KVM: introduce new mapping API for percpu mappings
Using virt_to_phys on percpu mappings is horribly wrong (my own bad).
Thankfully, the kernel offers a way to obtain the phisical address
of such a mapping.
Add a new "create_hyp_percpu_mappings" to deal with those.
*Fully untested, don't merge*
Not-Even-Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
---
arch/arm/include/asm/kvm_mmu.h | 1 +
arch/arm/kvm/arm.c | 2 +-
arch/arm/kvm/mmu.c | 20 ++++++++++++++++++++
arch/arm64/include/asm/kvm_mmu.h | 1 +
4 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index 9b28c41..6dcb9ff 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -43,6 +43,7 @@
#include <asm/pgalloc.h>
int create_hyp_mappings(void *from, void *to);
+int create_hyp_percpu_mappings(void *from, void *to);
int create_hyp_io_mappings(void *from, void *to, phys_addr_t);
void free_boot_hyp_pgd(void);
void free_hyp_pgds(void);
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 9c697db..6191960 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -911,7 +911,7 @@ static int init_hyp_mode(void)
kvm_cpu_context_t *cpu_ctxt;
cpu_ctxt = per_cpu_ptr(kvm_host_cpu_state, cpu);
- err = create_hyp_mappings(cpu_ctxt, cpu_ctxt + 1);
+ err = create_hyp_percpu_mappings(cpu_ctxt, cpu_ctxt + 1);
if (err) {
kvm_err("Cannot map host CPU state: %d\n", err);
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index b0de86b..e509718 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -331,6 +331,26 @@ int create_hyp_mappings(void *from, void *to)
}
/**
+ * create_hyp_percpu_mappings - duplicate a percpu kernel virtual address
+ * range in Hyp mode
+ * @from: The virtual kernel start address of the range
+ * @to: The virtual kernel end address of the range (exclusive)
+ *
+ * The same virtual address as the kernel virtual address is also used
+ * in Hyp-mode mapping (modulo HYP_PAGE_OFFSET) to the same underlying
+ * physical pages. It *has* to be a percpu pointer.
+ */
+int create_hyp_percpu_mappings(void *from, void *to)
+{
+ unsigned long phys_addr = per_cpu_ptr_to_phys(from);
+ unsigned long start = KERN_TO_HYP((unsigned long)from);
+ unsigned long end = KERN_TO_HYP((unsigned long)to);
+
+ return __create_hyp_mappings(hyp_pgd, start, end,
+ __phys_to_pfn(phys_addr), PAGE_HYP);
+}
+
+/**
* create_hyp_io_mappings - duplicate a kernel IO mapping into Hyp mode
* @from: The kernel start VA of the range
* @to: The kernel end VA of the range (exclusive)
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index efe609c..a97a92d 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -71,6 +71,7 @@
#define S2_PGD_ORDER get_order(PTRS_PER_S2_PGD * sizeof(pgd_t))
int create_hyp_mappings(void *from, void *to);
+int create_hyp_percpu_mappings(void *from, void *to);
int create_hyp_io_mappings(void *from, void *to, phys_addr_t);
void free_boot_hyp_pgd(void);
void free_hyp_pgds(void);
--
1.8.2.3
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