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[PATCH v2] riscv: mm: Fix alignment of phys_ram_base

Xu Lu posted 1 patch 1 year ago 
arch/riscv/mm/init.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
[PATCH v2] riscv: mm: Fix alignment of phys_ram_base
Posted by Xu Lu 1 year ago 
This commit fixes the alignment of phys_ram_base in RISC-V.

In sparse vmemmap model, the virtual address of vmemmap is calculated as:
((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT)).
And the struct page's va can be calculated with an offset:
(vmemmap + (pfn)).

However, when initializing struct pages, kernel actually starts from the
first page from the same section that phys_ram_base belongs to. If the
first page's physical address is not (phys_ram_base >> PAGE_SHIFT), then
we get an va below VMEMMAP_START when calculating va for it's struct page.

For example, if phys_ram_base starts from 0x82000000 with pfn 0x82000, the
first page in the same section is actually pfn 0x80000. During
init_unavailable_range(), we will initialize struct page for pfn 0x80000
with virtual address ((struct page *)VMEMMAP_START - 0x2000), which is
below VMEMMAP_START as well as PCI_IO_END.

This commit fixes this bug by aligning phys_ram_base with SECTION_SIZE.

Fixes: c3bcc65d4d2e ("riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping")
Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
---
 arch/riscv/mm/init.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 0e8c20adcd98..974cafa7c85e 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -33,6 +33,9 @@
 #include <asm/pgtable.h>
 #include <asm/sections.h>
 #include <asm/soc.h>
+#ifdef CONFIG_SPARSEMEM
+#include <asm/sparsemem.h>
+#endif
 #include <asm/tlbflush.h>
 
 #include "../kernel/head.h"
@@ -59,6 +62,12 @@ EXPORT_SYMBOL(pgtable_l4_enabled);
 EXPORT_SYMBOL(pgtable_l5_enabled);
 #endif
 
+#ifdef CONFIG_SPARSEMEM
+#define RISCV_MEMSTART_ALIGN	(1UL << SECTION_SIZE_BITS)
+#else
+#define RISCV_MEMSTART_ALIGN	PMD_SIZE
+#endif
+
 phys_addr_t phys_ram_base __ro_after_init;
 EXPORT_SYMBOL(phys_ram_base);
 
@@ -239,9 +248,13 @@ static void __init setup_bootmem(void)
 	/*
 	 * Make sure we align the start of the memory on a PMD boundary so that
 	 * at worst, we map the linear mapping with PMD mappings.
+	 *
+	 * Also, make sure we align the start of the memory on a SECTION boundary
+	 * when CONFIG_SPARSEMEM_VMEMMAP is enabled to ensure the correctness of
+	 * pfn_to_page().
 	 */
 	if (!IS_ENABLED(CONFIG_XIP_KERNEL))
-		phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
+		phys_ram_base = round_down(memblock_start_of_DRAM(), RISCV_MEMSTART_ALIGN);
 
 	/*
 	 * In 64-bit, any use of __va/__pa before this point is wrong as we
-- 
2.20.1
Re: [PATCH v2] riscv: mm: Fix alignment of phys_ram_base
Posted by Alexandre Ghiti 1 year ago 
Hi Xu,

On 03/12/2024 15:49, Xu Lu wrote:
> This commit fixes the alignment of phys_ram_base in RISC-V.
>
> In sparse vmemmap model, the virtual address of vmemmap is calculated as:
> ((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT)).
> And the struct page's va can be calculated with an offset:
> (vmemmap + (pfn)).
>
> However, when initializing struct pages, kernel actually starts from the
> first page from the same section that phys_ram_base belongs to. If the
> first page's physical address is not (phys_ram_base >> PAGE_SHIFT), then
> we get an va below VMEMMAP_START when calculating va for it's struct page.
>
> For example, if phys_ram_base starts from 0x82000000 with pfn 0x82000, the
> first page in the same section is actually pfn 0x80000. During
> init_unavailable_range(), we will initialize struct page for pfn 0x80000
> with virtual address ((struct page *)VMEMMAP_START - 0x2000), which is
> below VMEMMAP_START as well as PCI_IO_END.
>
> This commit fixes this bug by aligning phys_ram_base with SECTION_SIZE.
>
> Fixes: c3bcc65d4d2e ("riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping")
> Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
> ---
>   arch/riscv/mm/init.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 0e8c20adcd98..974cafa7c85e 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -33,6 +33,9 @@
>   #include <asm/pgtable.h>
>   #include <asm/sections.h>
>   #include <asm/soc.h>
> +#ifdef CONFIG_SPARSEMEM
> +#include <asm/sparsemem.h>
> +#endif
>   #include <asm/tlbflush.h>
>   
>   #include "../kernel/head.h"
> @@ -59,6 +62,12 @@ EXPORT_SYMBOL(pgtable_l4_enabled);
>   EXPORT_SYMBOL(pgtable_l5_enabled);
>   #endif
>   
> +#ifdef CONFIG_SPARSEMEM
> +#define RISCV_MEMSTART_ALIGN	(1UL << SECTION_SIZE_BITS)
> +#else
> +#define RISCV_MEMSTART_ALIGN	PMD_SIZE
> +#endif
> +
>   phys_addr_t phys_ram_base __ro_after_init;
>   EXPORT_SYMBOL(phys_ram_base);
>   
> @@ -239,9 +248,13 @@ static void __init setup_bootmem(void)
>   	/*
>   	 * Make sure we align the start of the memory on a PMD boundary so that
>   	 * at worst, we map the linear mapping with PMD mappings.
> +	 *
> +	 * Also, make sure we align the start of the memory on a SECTION boundary
> +	 * when CONFIG_SPARSEMEM_VMEMMAP is enabled to ensure the correctness of
> +	 * pfn_to_page().
>   	 */
>   	if (!IS_ENABLED(CONFIG_XIP_KERNEL))
> -		phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
> +		phys_ram_base = round_down(memblock_start_of_DRAM(), RISCV_MEMSTART_ALIGN);
>   
>   	/*
>   	 * In 64-bit, any use of __va/__pa before this point is wrong as we


That's a good catch indeed. But I'm wondering if it would be more 
correct to fix the macro vmemmap instead of phys_ram_base since 
phys_ram_base is supposed to hold the real base of the system memory, 
which would be wrong with your patch. I mean something like that instead 
(or similar, I haven't tested):

#define vmemmap         ((struct page *)VMEMMAP_START - 
(round_down(memblock_start_of_DRAM(), RISCV_MEMSTART_ALIGN) >> PAGE_SHIFT))

And the fixes tag should be:

Fixes: a11dd49dcb93 ("riscv: Sparse-Memory/vmemmap out-of-bounds fix")

Thanks,

Alex
Re: [External] Re: [PATCH v2] riscv: mm: Fix alignment of phys_ram_base
Posted by Xu Lu 1 year ago 
Hi Alex,

On Thu, Dec 5, 2024 at 10:34 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> Hi Xu,
>
> On 03/12/2024 15:49, Xu Lu wrote:
> > This commit fixes the alignment of phys_ram_base in RISC-V.
> >
> > In sparse vmemmap model, the virtual address of vmemmap is calculated as:
> > ((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT)).
> > And the struct page's va can be calculated with an offset:
> > (vmemmap + (pfn)).
> >
> > However, when initializing struct pages, kernel actually starts from the
> > first page from the same section that phys_ram_base belongs to. If the
> > first page's physical address is not (phys_ram_base >> PAGE_SHIFT), then
> > we get an va below VMEMMAP_START when calculating va for it's struct page.
> >
> > For example, if phys_ram_base starts from 0x82000000 with pfn 0x82000, the
> > first page in the same section is actually pfn 0x80000. During
> > init_unavailable_range(), we will initialize struct page for pfn 0x80000
> > with virtual address ((struct page *)VMEMMAP_START - 0x2000), which is
> > below VMEMMAP_START as well as PCI_IO_END.
> >
> > This commit fixes this bug by aligning phys_ram_base with SECTION_SIZE.
> >
> > Fixes: c3bcc65d4d2e ("riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping")
> > Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
> > ---
> >   arch/riscv/mm/init.c | 15 ++++++++++++++-
> >   1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 0e8c20adcd98..974cafa7c85e 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -33,6 +33,9 @@
> >   #include <asm/pgtable.h>
> >   #include <asm/sections.h>
> >   #include <asm/soc.h>
> > +#ifdef CONFIG_SPARSEMEM
> > +#include <asm/sparsemem.h>
> > +#endif
> >   #include <asm/tlbflush.h>
> >
> >   #include "../kernel/head.h"
> > @@ -59,6 +62,12 @@ EXPORT_SYMBOL(pgtable_l4_enabled);
> >   EXPORT_SYMBOL(pgtable_l5_enabled);
> >   #endif
> >
> > +#ifdef CONFIG_SPARSEMEM
> > +#define RISCV_MEMSTART_ALIGN (1UL << SECTION_SIZE_BITS)
> > +#else
> > +#define RISCV_MEMSTART_ALIGN PMD_SIZE
> > +#endif
> > +
> >   phys_addr_t phys_ram_base __ro_after_init;
> >   EXPORT_SYMBOL(phys_ram_base);
> >
> > @@ -239,9 +248,13 @@ static void __init setup_bootmem(void)
> >       /*
> >        * Make sure we align the start of the memory on a PMD boundary so that
> >        * at worst, we map the linear mapping with PMD mappings.
> > +      *
> > +      * Also, make sure we align the start of the memory on a SECTION boundary
> > +      * when CONFIG_SPARSEMEM_VMEMMAP is enabled to ensure the correctness of
> > +      * pfn_to_page().
> >        */
> >       if (!IS_ENABLED(CONFIG_XIP_KERNEL))
> > -             phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
> > +             phys_ram_base = round_down(memblock_start_of_DRAM(), RISCV_MEMSTART_ALIGN);
> >
> >       /*
> >        * In 64-bit, any use of __va/__pa before this point is wrong as we
>
>
> That's a good catch indeed. But I'm wondering if it would be more
> correct to fix the macro vmemmap instead of phys_ram_base since
> phys_ram_base is supposed to hold the real base of the system memory,
> which would be wrong with your patch. I mean something like that instead
> (or similar, I haven't tested):
>
> #define vmemmap         ((struct page *)VMEMMAP_START -
> (round_down(memblock_start_of_DRAM(), RISCV_MEMSTART_ALIGN) >> PAGE_SHIFT))

Thanks for your comment.

Good idea. I have thought about this. But I wasn't sure if it's OK to
introduce extra calculation whenever pfn_to_page() and page_to_pfn()
is called. So I referred to ARM which aligns memstart_addr with
SECTION size too and then made a similar modification.

If it is not appropriate to change the semantics of phys_ram_base, how
about introducing a new variable vmemmap_start_addr and use it to
calculate vmemmap:

#define vmemmap         ((struct page *)VMEMMAP_START -
(vmemmap_start_addr >> PAGE_SHIFT))

Best Regards,

Xu Lu

>
> And the fixes tag should be:
>
> Fixes: a11dd49dcb93 ("riscv: Sparse-Memory/vmemmap out-of-bounds fix")
>
> Thanks,
>
> Alex
>
Re: [External] Re: [PATCH v2] riscv: mm: Fix alignment of phys_ram_base
Posted by Alexandre Ghiti 1 year ago 
Hi Xu,

On 06/12/2024 04:11, Xu Lu wrote:
> Hi Alex,
>
> On Thu, Dec 5, 2024 at 10:34 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>> Hi Xu,
>>
>> On 03/12/2024 15:49, Xu Lu wrote:
>>> This commit fixes the alignment of phys_ram_base in RISC-V.
>>>
>>> In sparse vmemmap model, the virtual address of vmemmap is calculated as:
>>> ((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT)).
>>> And the struct page's va can be calculated with an offset:
>>> (vmemmap + (pfn)).
>>>
>>> However, when initializing struct pages, kernel actually starts from the
>>> first page from the same section that phys_ram_base belongs to. If the
>>> first page's physical address is not (phys_ram_base >> PAGE_SHIFT), then
>>> we get an va below VMEMMAP_START when calculating va for it's struct page.
>>>
>>> For example, if phys_ram_base starts from 0x82000000 with pfn 0x82000, the
>>> first page in the same section is actually pfn 0x80000. During
>>> init_unavailable_range(), we will initialize struct page for pfn 0x80000
>>> with virtual address ((struct page *)VMEMMAP_START - 0x2000), which is
>>> below VMEMMAP_START as well as PCI_IO_END.
>>>
>>> This commit fixes this bug by aligning phys_ram_base with SECTION_SIZE.
>>>
>>> Fixes: c3bcc65d4d2e ("riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping")
>>> Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
>>> ---
>>>    arch/riscv/mm/init.c | 15 ++++++++++++++-
>>>    1 file changed, 14 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>>> index 0e8c20adcd98..974cafa7c85e 100644
>>> --- a/arch/riscv/mm/init.c
>>> +++ b/arch/riscv/mm/init.c
>>> @@ -33,6 +33,9 @@
>>>    #include <asm/pgtable.h>
>>>    #include <asm/sections.h>
>>>    #include <asm/soc.h>
>>> +#ifdef CONFIG_SPARSEMEM
>>> +#include <asm/sparsemem.h>
>>> +#endif
>>>    #include <asm/tlbflush.h>
>>>
>>>    #include "../kernel/head.h"
>>> @@ -59,6 +62,12 @@ EXPORT_SYMBOL(pgtable_l4_enabled);
>>>    EXPORT_SYMBOL(pgtable_l5_enabled);
>>>    #endif
>>>
>>> +#ifdef CONFIG_SPARSEMEM
>>> +#define RISCV_MEMSTART_ALIGN (1UL << SECTION_SIZE_BITS)
>>> +#else
>>> +#define RISCV_MEMSTART_ALIGN PMD_SIZE
>>> +#endif
>>> +
>>>    phys_addr_t phys_ram_base __ro_after_init;
>>>    EXPORT_SYMBOL(phys_ram_base);
>>>
>>> @@ -239,9 +248,13 @@ static void __init setup_bootmem(void)
>>>        /*
>>>         * Make sure we align the start of the memory on a PMD boundary so that
>>>         * at worst, we map the linear mapping with PMD mappings.
>>> +      *
>>> +      * Also, make sure we align the start of the memory on a SECTION boundary
>>> +      * when CONFIG_SPARSEMEM_VMEMMAP is enabled to ensure the correctness of
>>> +      * pfn_to_page().
>>>         */
>>>        if (!IS_ENABLED(CONFIG_XIP_KERNEL))
>>> -             phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
>>> +             phys_ram_base = round_down(memblock_start_of_DRAM(), RISCV_MEMSTART_ALIGN);
>>>
>>>        /*
>>>         * In 64-bit, any use of __va/__pa before this point is wrong as we
>>
>> That's a good catch indeed. But I'm wondering if it would be more
>> correct to fix the macro vmemmap instead of phys_ram_base since
>> phys_ram_base is supposed to hold the real base of the system memory,
>> which would be wrong with your patch. I mean something like that instead
>> (or similar, I haven't tested):
>>
>> #define vmemmap         ((struct page *)VMEMMAP_START -
>> (round_down(memblock_start_of_DRAM(), RISCV_MEMSTART_ALIGN) >> PAGE_SHIFT))
> Thanks for your comment.
>
> Good idea. I have thought about this. But I wasn't sure if it's OK to
> introduce extra calculation whenever pfn_to_page() and page_to_pfn()
> is called. So I referred to ARM which aligns memstart_addr with
> SECTION size too and then made a similar modification.
>
> If it is not appropriate to change the semantics of phys_ram_base, how
> about introducing a new variable vmemmap_start_addr and use it to
> calculate vmemmap:
>
> #define vmemmap         ((struct page *)VMEMMAP_START -
> (vmemmap_start_addr >> PAGE_SHIFT))


I agree, that's a good idea to introduce vmemmap_start_addr.

Thanks,

Alex


>
> Best Regards,
>
> Xu Lu
>
>> And the fixes tag should be:
>>
>> Fixes: a11dd49dcb93 ("riscv: Sparse-Memory/vmemmap out-of-bounds fix")
>>
>> Thanks,
>>
>> Alex
>>
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> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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