Re: [PATCH 2/8] x86/head: Refactor 32-bit pgtable setup

[Boris Ostrovsky]

On 10/14/2016 02:05 PM, Boris Ostrovsky wrote:
> From: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
> ---
>  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