[Xen-devel] xen/arm: Stop relocating Xen

At the moment, Xen is relocated towards the end of the memory. While
this has the advantage to free space in low memory, the code is not
compliant with the break-before-make because it requires to switch
between two sets of page-table. This is not entirely trivial to fix as
it would require us to go through an identity mapping and disabling MMU.

Furtheremore, it looks like that some platform (such as the Hikey960)
may not be able to bring-up secondary CPUs if the entry is too high.

I don't believe the low memory is an issue because Xen is quite tiny
(< 2MB). So the best solution is to stop relocating Xen. This has the
advantage to simplify the code.

Note that the break-before-make issue is not fixed by this patch.

Signed-off-by: Julien Grall <julien.grall@arm.com>
---
 xen/arch/arm/arm32/head.S | 54 +++------------------------------------
 xen/arch/arm/arm64/head.S | 50 +++++-------------------------------
 xen/arch/arm/mm.c         | 22 +++++-----------
 xen/arch/arm/setup.c      | 65 +++--------------------------------------------
 xen/include/asm-arm/mm.h  |  2 +-
 5 files changed, 19 insertions(+), 174 deletions(-)

Please ignore this one. I used the wrong e-mail address.

Sorry for the noise.

On 11/22/18 8:46 PM, Julien Grall wrote:
> At the moment, Xen is relocated towards the end of the memory. While
> this has the advantage to free space in low memory, the code is not
> compliant with the break-before-make because it requires to switch
> between two sets of page-table. This is not entirely trivial to fix as
> it would require us to go through an identity mapping and disabling MMU.
> 
> Furtheremore, it looks like that some platform (such as the Hikey960)
> may not be able to bring-up secondary CPUs if the entry is too high.
> 
> I don't believe the low memory is an issue because Xen is quite tiny
> (< 2MB). So the best solution is to stop relocating Xen. This has the
> advantage to simplify the code.
> 
> Note that the break-before-make issue is not fixed by this patch.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>
> ---
>   xen/arch/arm/arm32/head.S | 54 +++------------------------------------
>   xen/arch/arm/arm64/head.S | 50 +++++-------------------------------
>   xen/arch/arm/mm.c         | 22 +++++-----------
>   xen/arch/arm/setup.c      | 65 +++--------------------------------------------
>   xen/include/asm-arm/mm.h  |  2 +-
>   5 files changed, 19 insertions(+), 174 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 93b51e9ef2..390a505e05 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -469,58 +469,12 @@ fail:   PRINT("- Boot failed -\r\n")
>   GLOBAL(_end_boot)
>   
>   /*
> - * Copy Xen to new location and switch TTBR
> + * Switch TTBR
>    * r1:r0       ttbr
> - * r2          source address
> - * r3          destination address
> - * [sp]=>r4    length
>    *
> - * Source and destination must be word aligned, length is rounded up
> - * to a 16 byte boundary.
> - *
> - * MUST BE VERY CAREFUL when saving things to RAM over the copy
> + * TODO: This code does not comply with break-before-make.
>    */
> -ENTRY(relocate_xen)
> -        push {r4,r5,r6,r7,r8,r9,r10,r11}
> -
> -        ldr   r4, [sp, #8*4]                /* Get 4th argument from stack */
> -
> -        /* Copy 16 bytes at a time using:
> -         * r5:  counter
> -         * r6:  data
> -         * r7:  data
> -         * r8:  data
> -         * r9:  data
> -         * r10: source
> -         * r11: destination
> -         */
> -        mov   r5, r4
> -        mov   r10, r2
> -        mov   r11, r3
> -1:      ldmia r10!, {r6, r7, r8, r9}
> -        stmia r11!, {r6, r7, r8, r9}
> -
> -        subs  r5, r5, #16
> -        bgt   1b
> -
> -        /* Flush destination from dcache using:
> -         * r5: counter
> -         * r6: step
> -         * r7: vaddr
> -         */
> -        dsb        /* So the CPU issues all writes to the range */
> -
> -        mov   r5, r4
> -        ldr   r6, =dcache_line_bytes /* r6 := step */
> -        ldr   r6, [r6]
> -        mov   r7, r3
> -
> -1:      mcr   CP32(r7, DCCMVAC)
> -
> -        add   r7, r7, r6
> -        subs  r5, r5, r6
> -        bgt   1b
> -
> +ENTRY(switch_ttbr)
>           dsb                            /* Ensure the flushes happen before
>                                           * continuing */
>           isb                            /* Ensure synchronization with previous
> @@ -543,8 +497,6 @@ ENTRY(relocate_xen)
>           dsb                            /* Ensure completion of TLB+BP flush */
>           isb
>   
> -        pop {r4, r5,r6,r7,r8,r9,r10,r11}
> -
>           mov pc, lr
>   
>   #ifdef CONFIG_EARLY_PRINTK
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index 9428c3f5a2..4589a37874 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -605,52 +605,14 @@ fail:   PRINT("- Boot failed -\r\n")
>   
>   GLOBAL(_end_boot)
>   
> -/* Copy Xen to new location and switch TTBR
> - * x0    ttbr
> - * x1    source address
> - * x2    destination address
> - * x3    length
> +/*
> + * Switch TTBR
>    *
> - * Source and destination must be word aligned, length is rounded up
> - * to a 16 byte boundary.
> + * x0    ttbr
>    *
> - * MUST BE VERY CAREFUL when saving things to RAM over the copy */
> -ENTRY(relocate_xen)
> -        /* Copy 16 bytes at a time using:
> -         *   x9: counter
> -         *   x10: data
> -         *   x11: data
> -         *   x12: source
> -         *   x13: destination
> -         */
> -        mov     x9, x3
> -        mov     x12, x1
> -        mov     x13, x2
> -
> -1:      ldp     x10, x11, [x12], #16
> -        stp     x10, x11, [x13], #16
> -
> -        subs    x9, x9, #16
> -        bgt     1b
> -
> -        /* Flush destination from dcache using:
> -         * x9: counter
> -         * x10: step
> -         * x11: vaddr
> -         */
> -        dsb   sy        /* So the CPU issues all writes to the range */
> -
> -        mov   x9, x3
> -        ldr   x10, =dcache_line_bytes /* x10 := step */
> -        ldr   x10, [x10]
> -        mov   x11, x2
> -
> -1:      dc    cvac, x11
> -
> -        add   x11, x11, x10
> -        subs  x9, x9, x10
> -        bgt   1b
> -
> + * TODO: This code does not comply with break-before-make.
> + */
> +ENTRY(switch_ttbr)
>           dsb   sy                     /* Ensure the flushes happen before
>                                         * continuing */
>           isb                          /* Ensure synchronization with previous
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 987fcb9162..5f4fb09257 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -601,7 +601,7 @@ void __init remove_early_mappings(void)
>       flush_xen_data_tlb_range_va(BOOT_FDT_VIRT_START, BOOT_FDT_SLOT_SIZE);
>   }
>   
> -extern void relocate_xen(uint64_t ttbr, void *src, void *dst, size_t len);
> +extern void switch_ttbr(uint64_t ttbr);
>   
>   /* Clear a translation table and clean & invalidate the cache */
>   static void clear_table(void *table)
> @@ -612,15 +612,13 @@ static void clear_table(void *table)
>   
>   /* Boot-time pagetable setup.
>    * Changes here may need matching changes in head.S */
> -void __init setup_pagetables(unsigned long boot_phys_offset, paddr_t xen_paddr)
> +void __init setup_pagetables(unsigned long boot_phys_offset)
>   {
>       uint64_t ttbr;
> -    unsigned long dest_va;
>       lpae_t pte, *p;
>       int i;
>   
> -    /* Calculate virt-to-phys offset for the new location */
> -    phys_offset = xen_paddr - (unsigned long) _start;
> +    phys_offset = boot_phys_offset;
>   
>   #ifdef CONFIG_ARM_64
>       p = (void *) xen_pgtable;
> @@ -652,7 +650,7 @@ void __init setup_pagetables(unsigned long boot_phys_offset, paddr_t xen_paddr)
>       /* Initialise xen second level entries ... */
>       /* ... Xen's text etc */
>   
> -    pte = mfn_to_xen_entry(maddr_to_mfn(xen_paddr), MT_NORMAL);
> +    pte = pte_of_xenaddr((vaddr_t)_start);
>       pte.pt.xn = 0;/* Contains our text mapping! */
>       xen_second[second_table_offset(XEN_VIRT_START)] = pte;
>   
> @@ -667,21 +665,13 @@ void __init setup_pagetables(unsigned long boot_phys_offset, paddr_t xen_paddr)
>       pte = boot_second[second_table_offset(BOOT_FDT_VIRT_START + SZ_2M)];
>       xen_second[second_table_offset(BOOT_FDT_VIRT_START + SZ_2M)] = pte;
>   
> -    /* ... Boot Misc area for xen relocation */
> -    dest_va = BOOT_RELOC_VIRT_START;
> -    pte = mfn_to_xen_entry(maddr_to_mfn(xen_paddr), MT_NORMAL);
> -    /* Map the destination in xen_second. */
> -    xen_second[second_table_offset(dest_va)] = pte;
> -    /* Map the destination in boot_second. */
> -    write_pte(boot_second + second_table_offset(dest_va), pte);
> -    flush_xen_data_tlb_range_va_local(dest_va, SECOND_SIZE);
>   #ifdef CONFIG_ARM_64
>       ttbr = (uintptr_t) xen_pgtable + phys_offset;
>   #else
>       ttbr = (uintptr_t) cpu0_pgtable + phys_offset;
>   #endif
>   
> -    relocate_xen(ttbr, _start, (void*)dest_va, _end - _start);
> +    switch_ttbr(ttbr);
>   
>       /* Clear the copy of the boot pagetables. Each secondary CPU
>        * rebuilds these itself (see head.S) */
> @@ -696,7 +686,7 @@ void __init setup_pagetables(unsigned long boot_phys_offset, paddr_t xen_paddr)
>       /* Break up the Xen mapping into 4k pages and protect them separately. */
>       for ( i = 0; i < LPAE_ENTRIES; i++ )
>       {
> -        mfn_t mfn = mfn_add(maddr_to_mfn(xen_paddr), i);
> +        mfn_t mfn = mfn_add(maddr_to_mfn((vaddr_t)_start + phys_offset), i);
>           unsigned long va = XEN_VIRT_START + (i << PAGE_SHIFT);
>           if ( !is_kernel(va) )
>               break;
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index aec53f30d3..e84172fbc3 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -374,6 +374,7 @@ void __init discard_initial_modules(void)
>       remove_early_mappings();
>   }
>   
> +#ifdef CONFIG_ARM_32
>   /*
>    * Returns the end address of the highest region in the range s..e
>    * with required size and alignment that does not conflict with the
> @@ -440,6 +441,7 @@ static paddr_t __init consider_modules(paddr_t s, paddr_t e,
>       }
>       return e;
>   }
> +#endif
>   
>   /*
>    * Return the end of the non-module region starting at s. In other
> @@ -475,59 +477,6 @@ static paddr_t __init next_module(paddr_t s, paddr_t *end)
>       return lowest;
>   }
>   
> -
> -/**
> - * get_xen_paddr - get physical address to relocate Xen to
> - *
> - * Xen is relocated to as near to the top of RAM as possible and
> - * aligned to a XEN_PADDR_ALIGN boundary.
> - */
> -static paddr_t __init get_xen_paddr(void)
> -{
> -    struct meminfo *mi = &bootinfo.mem;
> -    paddr_t min_size;
> -    paddr_t paddr = 0;
> -    int i;
> -
> -    min_size = (_end - _start + (XEN_PADDR_ALIGN-1)) & ~(XEN_PADDR_ALIGN-1);
> -
> -    /* Find the highest bank with enough space. */
> -    for ( i = 0; i < mi->nr_banks; i++ )
> -    {
> -        const struct membank *bank = &mi->bank[i];
> -        paddr_t s, e;
> -
> -        if ( bank->size >= min_size )
> -        {
> -            e = consider_modules(bank->start, bank->start + bank->size,
> -                                 min_size, XEN_PADDR_ALIGN, 0);
> -            if ( !e )
> -                continue;
> -
> -#ifdef CONFIG_ARM_32
> -            /* Xen must be under 4GB */
> -            if ( e > 0x100000000ULL )
> -                e = 0x100000000ULL;
> -            if ( e < bank->start )
> -                continue;
> -#endif
> -
> -            s = e - min_size;
> -
> -            if ( s > paddr )
> -                paddr = s;
> -        }
> -    }
> -
> -    if ( !paddr )
> -        panic("Not enough memory to relocate Xen\n");
> -
> -    printk("Placing Xen at 0x%"PRIpaddr"-0x%"PRIpaddr"\n",
> -           paddr, paddr + min_size);
> -
> -    return paddr;
> -}
> -
>   static void __init init_pdx(void)
>   {
>       paddr_t bank_start, bank_size, bank_end;
> @@ -783,7 +732,6 @@ void __init start_xen(unsigned long boot_phys_offset,
>   {
>       size_t fdt_size;
>       int cpus, i;
> -    paddr_t xen_paddr;
>       const char *cmdline;
>       struct bootmodule *xen_bootmodule;
>       struct domain *dom0;
> @@ -827,14 +775,7 @@ void __init start_xen(unsigned long boot_phys_offset,
>                                (paddr_t)(uintptr_t)(_end - _start + 1), false);
>       BUG_ON(!xen_bootmodule);
>   
> -    xen_paddr = get_xen_paddr();
> -    setup_pagetables(boot_phys_offset, xen_paddr);
> -
> -    /* Update Xen's address now that we have relocated. */
> -    printk("Update BOOTMOD_XEN from %"PRIpaddr"-%"PRIpaddr" => %"PRIpaddr"-%"PRIpaddr"\n",
> -           xen_bootmodule->start, xen_bootmodule->start + xen_bootmodule->size,
> -           xen_paddr, xen_paddr + xen_bootmodule->size);
> -    xen_bootmodule->start = xen_paddr;
> +    setup_pagetables(boot_phys_offset);
>   
>       setup_mm(fdt_paddr, fdt_size);
>   
> diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
> index 940b74be33..129404b196 100644
> --- a/xen/include/asm-arm/mm.h
> +++ b/xen/include/asm-arm/mm.h
> @@ -169,7 +169,7 @@ extern unsigned long total_pages;
>   #define PDX_GROUP_SHIFT SECOND_SHIFT
>   
>   /* Boot-time pagetable setup */
> -extern void setup_pagetables(unsigned long boot_phys_offset, paddr_t xen_paddr);
> +extern void setup_pagetables(unsigned long boot_phys_offset);
>   /* Map FDT in boot pagetable */
>   extern void *early_fdt_map(paddr_t fdt_paddr);
>   /* Remove early mappings */
>