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xen/arm: Stop relocating Xen

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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.

Furthermore, 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.

While Xen should be quite tiny (< 2MB), the current algorithm to
allocate Dom0 memory will allocate memory chunks of at least 128MB.
Those memory chunks will always be 128MB. This means that depending on
where the modules are loaded, an extra 128MB may disappear.

As there are up to 4 modules (initramfs, XSM, kernel, DTB) loaded in
low memory. The problem is not entirely new as you could already waste
512MB of low-memory. The right solution would be to fix the allocation
algorithm. But this is independent from this patch.

For user in control of the memory (such as in U-boot), all modules
should be loaded as much as possible together or outside low-memory (i.e
above 4GB). For other users (i.e Grub/UEFI), I believe the bootloader is
already keeping everything together.

Based on the above, it would be fine to stop relocating Xen. This has
the advantage to simplify the code and should speed-up the boot as
relocation is not necessary anymore.

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

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reported-by: Matthew Daley <mattd@bugfuzz.com>
Tested-by: Matthew Daley <mattd@bugfuzz.com>
Tested-by: Andrii Anisov <andrii_anisov@epam.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
This commit is contained in:
Julien Grall authored and Stefano Stabellini committed 2018-12-18 14:45:00 -08:00
1 parent 2148a125b7
commit f60658c6ae
5 files changed
+17 -172
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xen/arch/arm/arm32/head.S
+3 -51
View File
@@ -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
xen/arch/arm/arm64/head.S
+6 -44
View File
@@ -609,52 +609,14 @@ fail: PRINT("- Boot failed -\r\n")
GLOBAL(_end_boot)
/* Copy Xen to new location and switch TTBR
/*
* Switch TTBR
*
* x0 ttbr
* x1 source address
* x2 destination address
* x3 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 */
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
xen/arch/arm/mm.c
+4 -14
View File
@@ -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;
@@ -686,21 +684,13 @@ 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) */
xen/arch/arm/setup.c
+3 -62
View File
@@ -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);
xen/include/asm-arm/mm.h
+1 -1
View File
@@ -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 */
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