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SubjectRe: [PATCH 2/8] x86/head: Refactor 32-bit pgtable setup
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On 10/14/2016 02:05 PM, Boris Ostrovsky wrote:
> From: Matt Fleming <matt@codeblueprint.co.uk>
>
> The new Xen PVH entry point requires page tables to be setup by the
> kernel since it is entered with paging disabled.
>
> Pull the common code out of head_32.S and into pgtable_32.S so that
> setup_pgtable_32 can be invoked from both the new Xen entry point and
> the existing startup_32 code.


Ping to x86 maintainers.

Peter, you had questions about this patch. Did I answer them?

-boris


>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
> ---
> arch/x86/Makefile | 2 +
> arch/x86/kernel/Makefile | 2 +
> arch/x86/kernel/head_32.S | 168 +------------------------------------
> arch/x86/kernel/pgtable_32.S | 196 +++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 201 insertions(+), 167 deletions(-)
> create mode 100644 arch/x86/kernel/pgtable_32.S
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 2d44933..67cc771 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -204,6 +204,8 @@ head-y += arch/x86/kernel/head$(BITS).o
> head-y += arch/x86/kernel/ebda.o
> head-y += arch/x86/kernel/platform-quirks.o
>
> +head-$(CONFIG_X86_32) += arch/x86/kernel/pgtable_32.o
> +
> libs-y += arch/x86/lib/
>
> # See arch/x86/Kbuild for content of core part of the kernel
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 4dd5d50..eae85a5 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -8,6 +8,8 @@ extra-y += ebda.o
> extra-y += platform-quirks.o
> extra-y += vmlinux.lds
>
> +extra-$(CONFIG_X86_32) += pgtable_32.o
> +
> CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE)
>
> ifdef CONFIG_FUNCTION_TRACER
> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
> index 5f40126..0db066e 100644
> --- a/arch/x86/kernel/head_32.S
> +++ b/arch/x86/kernel/head_32.S
> @@ -41,51 +41,6 @@
> #define X86_VENDOR_ID new_cpu_data+CPUINFO_x86_vendor_id
>
> /*
> - * This is how much memory in addition to the memory covered up to
> - * and including _end we need mapped initially.
> - * We need:
> - * (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)
> - * (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)
> - *
> - * Modulo rounding, each megabyte assigned here requires a kilobyte of
> - * memory, which is currently unreclaimed.
> - *
> - * This should be a multiple of a page.
> - *
> - * KERNEL_IMAGE_SIZE should be greater than pa(_end)
> - * and small than max_low_pfn, otherwise will waste some page table entries
> - */
> -
> -#if PTRS_PER_PMD > 1
> -#define PAGE_TABLE_SIZE(pages) (((pages) / PTRS_PER_PMD) + PTRS_PER_PGD)
> -#else
> -#define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)
> -#endif
> -
> -/*
> - * Number of possible pages in the lowmem region.
> - *
> - * We shift 2 by 31 instead of 1 by 32 to the left in order to avoid a
> - * gas warning about overflowing shift count when gas has been compiled
> - * with only a host target support using a 32-bit type for internal
> - * representation.
> - */
> -LOWMEM_PAGES = (((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT)
> -
> -/* Enough space to fit pagetables for the low memory linear map */
> -MAPPING_BEYOND_END = PAGE_TABLE_SIZE(LOWMEM_PAGES) << PAGE_SHIFT
> -
> -/*
> - * Worst-case size of the kernel mapping we need to make:
> - * a relocatable kernel can live anywhere in lowmem, so we need to be able
> - * to map all of lowmem.
> - */
> -KERNEL_PAGES = LOWMEM_PAGES
> -
> -INIT_MAP_SIZE = PAGE_TABLE_SIZE(KERNEL_PAGES) * PAGE_SIZE
> -RESERVE_BRK(pagetables, INIT_MAP_SIZE)
> -
> -/*
> * 32-bit kernel entrypoint; only used by the boot CPU. On entry,
> * %esi points to the real-mode code as a 32-bit pointer.
> * CS and DS must be 4 GB flat segments, but we don't depend on
> @@ -157,92 +112,7 @@ ENTRY(startup_32)
> call load_ucode_bsp
> #endif
>
> -/*
> - * Initialize page tables. This creates a PDE and a set of page
> - * tables, which are located immediately beyond __brk_base. The variable
> - * _brk_end is set up to point to the first "safe" location.
> - * Mappings are created both at virtual address 0 (identity mapping)
> - * and PAGE_OFFSET for up to _end.
> - */
> -#ifdef CONFIG_X86_PAE
> -
> - /*
> - * In PAE mode initial_page_table is statically defined to contain
> - * enough entries to cover the VMSPLIT option (that is the top 1, 2 or 3
> - * entries). The identity mapping is handled by pointing two PGD entries
> - * to the first kernel PMD.
> - *
> - * Note the upper half of each PMD or PTE are always zero at this stage.
> - */
> -
> -#define KPMDS (((-__PAGE_OFFSET) >> 30) & 3) /* Number of kernel PMDs */
> -
> - xorl %ebx,%ebx /* %ebx is kept at zero */
> -
> - movl $pa(__brk_base), %edi
> - movl $pa(initial_pg_pmd), %edx
> - movl $PTE_IDENT_ATTR, %eax
> -10:
> - leal PDE_IDENT_ATTR(%edi),%ecx /* Create PMD entry */
> - movl %ecx,(%edx) /* Store PMD entry */
> - /* Upper half already zero */
> - addl $8,%edx
> - movl $512,%ecx
> -11:
> - stosl
> - xchgl %eax,%ebx
> - stosl
> - xchgl %eax,%ebx
> - addl $0x1000,%eax
> - loop 11b
> -
> - /*
> - * End condition: we must map up to the end + MAPPING_BEYOND_END.
> - */
> - movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
> - cmpl %ebp,%eax
> - jb 10b
> -1:
> - addl $__PAGE_OFFSET, %edi
> - movl %edi, pa(_brk_end)
> - shrl $12, %eax
> - movl %eax, pa(max_pfn_mapped)
> -
> - /* Do early initialization of the fixmap area */
> - movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
> - movl %eax,pa(initial_pg_pmd+0x1000*KPMDS-8)
> -#else /* Not PAE */
> -
> -page_pde_offset = (__PAGE_OFFSET >> 20);
> -
> - movl $pa(__brk_base), %edi
> - movl $pa(initial_page_table), %edx
> - movl $PTE_IDENT_ATTR, %eax
> -10:
> - leal PDE_IDENT_ATTR(%edi),%ecx /* Create PDE entry */
> - movl %ecx,(%edx) /* Store identity PDE entry */
> - movl %ecx,page_pde_offset(%edx) /* Store kernel PDE entry */
> - addl $4,%edx
> - movl $1024, %ecx
> -11:
> - stosl
> - addl $0x1000,%eax
> - loop 11b
> - /*
> - * End condition: we must map up to the end + MAPPING_BEYOND_END.
> - */
> - movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
> - cmpl %ebp,%eax
> - jb 10b
> - addl $__PAGE_OFFSET, %edi
> - movl %edi, pa(_brk_end)
> - shrl $12, %eax
> - movl %eax, pa(max_pfn_mapped)
> -
> - /* Do early initialization of the fixmap area */
> - movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
> - movl %eax,pa(initial_page_table+0xffc)
> -#endif
> + call setup_pgtable_32
>
> #ifdef CONFIG_PARAVIRT
> /* This is can only trip for a broken bootloader... */
> @@ -660,47 +530,11 @@ ENTRY(setup_once_ref)
> */
> __PAGE_ALIGNED_BSS
> .align PAGE_SIZE
> -#ifdef CONFIG_X86_PAE
> -initial_pg_pmd:
> - .fill 1024*KPMDS,4,0
> -#else
> -ENTRY(initial_page_table)
> - .fill 1024,4,0
> -#endif
> -initial_pg_fixmap:
> - .fill 1024,4,0
> ENTRY(empty_zero_page)
> .fill 4096,1,0
> ENTRY(swapper_pg_dir)
> .fill 1024,4,0
>
> -/*
> - * This starts the data section.
> - */
> -#ifdef CONFIG_X86_PAE
> -__PAGE_ALIGNED_DATA
> - /* Page-aligned for the benefit of paravirt? */
> - .align PAGE_SIZE
> -ENTRY(initial_page_table)
> - .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0 /* low identity map */
> -# if KPMDS == 3
> - .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0
> - .long pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
> - .long pa(initial_pg_pmd+PGD_IDENT_ATTR+0x2000),0
> -# elif KPMDS == 2
> - .long 0,0
> - .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0
> - .long pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
> -# elif KPMDS == 1
> - .long 0,0
> - .long 0,0
> - .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0
> -# else
> -# error "Kernel PMDs should be 1, 2 or 3"
> -# endif
> - .align PAGE_SIZE /* needs to be page-sized too */
> -#endif
> -
> .data
> .balign 4
> ENTRY(initial_stack)
> diff --git a/arch/x86/kernel/pgtable_32.S b/arch/x86/kernel/pgtable_32.S
> new file mode 100644
> index 0000000..aded718
> --- /dev/null
> +++ b/arch/x86/kernel/pgtable_32.S
> @@ -0,0 +1,196 @@
> +#include <linux/threads.h>
> +#include <linux/init.h>
> +#include <linux/linkage.h>
> +#include <asm/segment.h>
> +#include <asm/page_types.h>
> +#include <asm/pgtable_types.h>
> +#include <asm/cache.h>
> +#include <asm/thread_info.h>
> +#include <asm/asm-offsets.h>
> +#include <asm/setup.h>
> +#include <asm/processor-flags.h>
> +#include <asm/msr-index.h>
> +#include <asm/cpufeatures.h>
> +#include <asm/percpu.h>
> +#include <asm/nops.h>
> +#include <asm/bootparam.h>
> +
> +/* Physical address */
> +#define pa(X) ((X) - __PAGE_OFFSET)
> +
> +/*
> + * This is how much memory in addition to the memory covered up to
> + * and including _end we need mapped initially.
> + * We need:
> + * (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)
> + * (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)
> + *
> + * Modulo rounding, each megabyte assigned here requires a kilobyte of
> + * memory, which is currently unreclaimed.
> + *
> + * This should be a multiple of a page.
> + *
> + * KERNEL_IMAGE_SIZE should be greater than pa(_end)
> + * and small than max_low_pfn, otherwise will waste some page table entries
> + */
> +
> +#if PTRS_PER_PMD > 1
> +#define PAGE_TABLE_SIZE(pages) (((pages) / PTRS_PER_PMD) + PTRS_PER_PGD)
> +#else
> +#define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)
> +#endif
> +
> +/*
> + * Number of possible pages in the lowmem region.
> + *
> + * We shift 2 by 31 instead of 1 by 32 to the left in order to avoid a
> + * gas warning about overflowing shift count when gas has been compiled
> + * with only a host target support using a 32-bit type for internal
> + * representation.
> + */
> +LOWMEM_PAGES = (((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT)
> +
> +/* Enough space to fit pagetables for the low memory linear map */
> +MAPPING_BEYOND_END = PAGE_TABLE_SIZE(LOWMEM_PAGES) << PAGE_SHIFT
> +
> +/*
> + * Worst-case size of the kernel mapping we need to make:
> + * a relocatable kernel can live anywhere in lowmem, so we need to be able
> + * to map all of lowmem.
> + */
> +KERNEL_PAGES = LOWMEM_PAGES
> +
> +INIT_MAP_SIZE = PAGE_TABLE_SIZE(KERNEL_PAGES) * PAGE_SIZE
> +RESERVE_BRK(pagetables, INIT_MAP_SIZE)
> +
> +/*
> + * Initialize page tables. This creates a PDE and a set of page
> + * tables, which are located immediately beyond __brk_base. The variable
> + * _brk_end is set up to point to the first "safe" location.
> + * Mappings are created both at virtual address 0 (identity mapping)
> + * and PAGE_OFFSET for up to _end.
> + */
> + .text
> +ENTRY(setup_pgtable_32)
> +#ifdef CONFIG_X86_PAE
> + /*
> + * In PAE mode initial_page_table is statically defined to contain
> + * enough entries to cover the VMSPLIT option (that is the top 1, 2 or 3
> + * entries). The identity mapping is handled by pointing two PGD entries
> + * to the first kernel PMD.
> + *
> + * Note the upper half of each PMD or PTE are always zero at this stage.
> + */
> +
> +#define KPMDS (((-__PAGE_OFFSET) >> 30) & 3) /* Number of kernel PMDs */
> +
> + xorl %ebx,%ebx /* %ebx is kept at zero */
> +
> + movl $pa(__brk_base), %edi
> + movl $pa(initial_pg_pmd), %edx
> + movl $PTE_IDENT_ATTR, %eax
> +10:
> + leal PDE_IDENT_ATTR(%edi),%ecx /* Create PMD entry */
> + movl %ecx,(%edx) /* Store PMD entry */
> + /* Upper half already zero */
> + addl $8,%edx
> + movl $512,%ecx
> +11:
> + stosl
> + xchgl %eax,%ebx
> + stosl
> + xchgl %eax,%ebx
> + addl $0x1000,%eax
> + loop 11b
> +
> + /*
> + * End condition: we must map up to the end + MAPPING_BEYOND_END.
> + */
> + movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
> + cmpl %ebp,%eax
> + jb 10b
> +1:
> + addl $__PAGE_OFFSET, %edi
> + movl %edi, pa(_brk_end)
> + shrl $12, %eax
> + movl %eax, pa(max_pfn_mapped)
> +
> + /* Do early initialization of the fixmap area */
> + movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
> + movl %eax,pa(initial_pg_pmd+0x1000*KPMDS-8)
> +#else /* Not PAE */
> +
> +page_pde_offset = (__PAGE_OFFSET >> 20);
> +
> + movl $pa(__brk_base), %edi
> + movl $pa(initial_page_table), %edx
> + movl $PTE_IDENT_ATTR, %eax
> +10:
> + leal PDE_IDENT_ATTR(%edi),%ecx /* Create PDE entry */
> + movl %ecx,(%edx) /* Store identity PDE entry */
> + movl %ecx,page_pde_offset(%edx) /* Store kernel PDE entry */
> + addl $4,%edx
> + movl $1024, %ecx
> +11:
> + stosl
> + addl $0x1000,%eax
> + loop 11b
> + /*
> + * End condition: we must map up to the end + MAPPING_BEYOND_END.
> + */
> + movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
> + cmpl %ebp,%eax
> + jb 10b
> + addl $__PAGE_OFFSET, %edi
> + movl %edi, pa(_brk_end)
> + shrl $12, %eax
> + movl %eax, pa(max_pfn_mapped)
> +
> + /* Do early initialization of the fixmap area */
> + movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
> + movl %eax,pa(initial_page_table+0xffc)
> +#endif
> + ret
> +ENDPROC(setup_pgtable_32)
> +
> +/*
> + * BSS section
> + */
> +__PAGE_ALIGNED_BSS
> + .align PAGE_SIZE
> +#ifdef CONFIG_X86_PAE
> +initial_pg_pmd:
> + .fill 1024*KPMDS,4,0
> +#else
> +ENTRY(initial_page_table)
> + .fill 1024,4,0
> +#endif
> +initial_pg_fixmap:
> + .fill 1024,4,0
> +
> +/*
> + * This starts the data section.
> + */
> +#ifdef CONFIG_X86_PAE
> +__PAGE_ALIGNED_DATA
> + /* Page-aligned for the benefit of paravirt? */
> + .align PAGE_SIZE
> +ENTRY(initial_page_table)
> + .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0 /* low identity map */
> +# if KPMDS == 3
> + .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0
> + .long pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
> + .long pa(initial_pg_pmd+PGD_IDENT_ATTR+0x2000),0
> +# elif KPMDS == 2
> + .long 0,0
> + .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0
> + .long pa(initial_pg_pmd+PGD_IDENT_ATTR+0x1000),0
> +# elif KPMDS == 1
> + .long 0,0
> + .long 0,0
> + .long pa(initial_pg_pmd+PGD_IDENT_ATTR),0
> +# else
> +# error "Kernel PMDs should be 1, 2 or 3"
> +# endif
> + .align PAGE_SIZE /* needs to be page-sized too */
> +#endif
>

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