The way how switch to virtual address was implemented in the
commit e66003e7be ("xen/riscv: introduce setup_initial_pages")
isn't safe enough as:
* enable_mmu() depends on hooking all exceptions
and pagefault.
* Any exception other than pagefault, or not taking a pagefault
causes it to malfunction, which means you will fail to boot
depending on where Xen was loaded into memory.
Instead of the proposed way of switching to virtual addresses was
decided to use identity mapping for area which constains needed code
to switch from identity mapping and after switching to virtual addresses,
identity mapping is removed from page-tables in the following way:
search for top-most page table entry and remove it.
Fixes: e66003e7be ("xen/riscv: introduce setup_initial_pages")
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
Changes in V5:
- update the algo of identity mapping removing.
- introduce IDENT_AREA_SIZE.
- introduce turn_on_mmu() function to enable and switch from 1:1 mapping.
- fix typo in PGTBL_INITIAL_COUNT define.
- update the comment above PGTBL_INITIAL_COUNT.
- update the commit message.
---
Changes in V4:
- remove definition of ARRAY_SIZE and ROUNDUP as <xen/macors.h> was introduced where these macros are located now.
- update definition of PGTBL_INITIAL_COUNT
- update the commit message
- update the algo of identity mapping removing
---
Changes in V3:
- remove unrelated to the patch changes ( SPDX tags in config.h ).
- update definition of PGTBL_INITIAL_COUNT taking into account identity mapping.
- refactor remove_identity_mapping() function.
- add explanatory comments in xen.lds.S and mm.c.
- update commit message.
- move save/restore of a0/a1 registers to [PATCH v2 2/3] xen/riscv: introduce
function for physical offset calculation.
---
Changes in V2:
- update definition of PGTBL_INITIAL_COUNT and the comment above.
- code style fixes.
- 1:1 mapping for entire Xen.
- remove id_addrs array becase entire Xen is mapped.
- reverse condition for cycle inside remove_identity_mapping().
- fix page table walk in remove_identity_mapping().
- update the commit message.
- add Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
- save hart_id and dtb_addr before call MMU related C functions.
- use phys_offset variable instead of doing calcultations to get phys offset
in head.S file. ( it can be easily done as entire Xen is 1:1 mapped )
- declare enable_muu() as __init.
---
xen/arch/riscv/include/asm/config.h | 2 +
xen/arch/riscv/include/asm/mm.h | 5 +-
xen/arch/riscv/mm.c | 90 +++++++++++++++--------------
xen/arch/riscv/riscv64/head.S | 32 ++++++++++
xen/arch/riscv/setup.c | 14 +----
xen/arch/riscv/xen.lds.S | 11 ++++
6 files changed, 99 insertions(+), 55 deletions(-)
diff --git a/xen/arch/riscv/include/asm/config.h b/xen/arch/riscv/include/asm/config.h
index fa90ae0898..f0544c6a20 100644
--- a/xen/arch/riscv/include/asm/config.h
+++ b/xen/arch/riscv/include/asm/config.h
@@ -95,6 +95,8 @@
#define RV_STAGE1_MODE SATP_MODE_SV32
#endif
+#define IDENT_AREA_SIZE 64
+
#endif /* __RISCV_CONFIG_H__ */
/*
* Local variables:
diff --git a/xen/arch/riscv/include/asm/mm.h b/xen/arch/riscv/include/asm/mm.h
index 7b94cbadd7..07c7a0abba 100644
--- a/xen/arch/riscv/include/asm/mm.h
+++ b/xen/arch/riscv/include/asm/mm.h
@@ -13,8 +13,11 @@ extern unsigned char cpu0_boot_stack[];
void setup_initial_pagetables(void);
void enable_mmu(void);
-void cont_after_mmu_is_enabled(void);
+
+void remove_identity_mapping(void);
unsigned long calc_phys_offset(void);
+void turn_on_mmu(unsigned long ra);
+
#endif /* _ASM_RISCV_MM_H */
diff --git a/xen/arch/riscv/mm.c b/xen/arch/riscv/mm.c
index 1df39ddf1b..d19fdb7878 100644
--- a/xen/arch/riscv/mm.c
+++ b/xen/arch/riscv/mm.c
@@ -4,6 +4,7 @@
#include <xen/compiler.h>
#include <xen/init.h>
#include <xen/kernel.h>
+#include <xen/macros.h>
#include <xen/pfn.h>
#include <asm/early_printk.h>
@@ -35,8 +36,11 @@ static unsigned long __ro_after_init phys_offset;
*
* It might be needed one more page table in case when Xen load address
* isn't 2 MB aligned.
+ *
+ * CONFIG_PAGING_LEVELS page tables are needed for the identity mapping,
+ * except that the root page table is shared with the initial mapping
*/
-#define PGTBL_INITIAL_COUNT ((CONFIG_PAGING_LEVELS - 1) + 1)
+#define PGTBL_INITIAL_COUNT ((CONFIG_PAGING_LEVELS - 1) * 2 + 1)
pte_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
stage1_pgtbl_root[PAGETABLE_ENTRIES];
@@ -75,6 +79,7 @@ static void __init setup_initial_mapping(struct mmu_desc *mmu_desc,
unsigned int index;
pte_t *pgtbl;
unsigned long page_addr;
+ bool is_identity_mapping = map_start == pa_start;
if ( (unsigned long)_start % XEN_PT_LEVEL_SIZE(0) )
{
@@ -108,16 +113,18 @@ static void __init setup_initial_mapping(struct mmu_desc *mmu_desc,
{
unsigned long paddr = (page_addr - map_start) + pa_start;
unsigned int permissions = PTE_LEAF_DEFAULT;
+ unsigned long addr = is_identity_mapping
+ ? page_addr : LINK_TO_LOAD(page_addr);
pte_t pte_to_be_written;
index = pt_index(0, page_addr);
- if ( is_kernel_text(LINK_TO_LOAD(page_addr)) ||
- is_kernel_inittext(LINK_TO_LOAD(page_addr)) )
- permissions =
- PTE_EXECUTABLE | PTE_READABLE | PTE_VALID;
+ if ( is_kernel_text(addr) ||
+ is_kernel_inittext(addr) )
+ permissions =
+ PTE_EXECUTABLE | PTE_READABLE | PTE_VALID;
- if ( is_kernel_rodata(LINK_TO_LOAD(page_addr)) )
+ if ( is_kernel_rodata(addr) )
permissions = PTE_READABLE | PTE_VALID;
pte_to_be_written = paddr_to_pte(paddr, permissions);
@@ -211,6 +218,13 @@ void __init setup_initial_pagetables(void)
unsigned long linker_start = LOAD_TO_LINK(load_start);
unsigned long linker_end = LOAD_TO_LINK(load_end);
+ unsigned long ident_start;
+ unsigned long ident_end;
+
+ /*
+ * If the overlapping check will be removed then remove_identity_mapping()
+ * logic should be updated.
+ */
if ( (linker_start != load_start) &&
(linker_start <= load_end) && (load_start <= linker_end) )
{
@@ -232,48 +246,40 @@ void __init setup_initial_pagetables(void)
linker_start,
linker_end,
load_start);
+
+ if ( linker_start == load_start )
+ return;
+
+ ident_start = (unsigned long)turn_on_mmu & XEN_PT_LEVEL_MAP_MASK(0);
+ ident_end = ident_start + PAGE_SIZE;
+
+ setup_initial_mapping(&mmu_desc,
+ ident_start,
+ ident_end,
+ ident_start);
}
-void __init noreturn noinline enable_mmu()
+void __init remove_identity_mapping(void)
{
- /*
- * Calculate a linker time address of the mmu_is_enabled
- * label and update CSR_STVEC with it.
- * MMU is configured in a way where linker addresses are mapped
- * on load addresses so in a case when linker addresses are not equal
- * to load addresses, after MMU is enabled, it will cause
- * an exception and jump to linker time addresses.
- * Otherwise if load addresses are equal to linker addresses the code
- * after mmu_is_enabled label will be executed without exception.
- */
- csr_write(CSR_STVEC, LOAD_TO_LINK((unsigned long)&&mmu_is_enabled));
-
- /* Ensure page table writes precede loading the SATP */
- sfence_vma();
+ unsigned int i;
+ pte_t *pgtbl;
+ unsigned int index, xen_index;
+ unsigned long ident_start =
+ LINK_TO_LOAD(turn_on_mmu) & XEN_PT_LEVEL_MAP_MASK(0);
- /* Enable the MMU and load the new pagetable for Xen */
- csr_write(CSR_SATP,
- PFN_DOWN((unsigned long)stage1_pgtbl_root) |
- RV_STAGE1_MODE << SATP_MODE_SHIFT);
+ for ( pgtbl = stage1_pgtbl_root, i = CONFIG_PAGING_LEVELS; i; i-- )
+ {
+ index = pt_index(i - 1, ident_start);
+ xen_index = pt_index(i - 1, XEN_VIRT_START);
- asm volatile ( ".p2align 2" );
- mmu_is_enabled:
- /*
- * Stack should be re-inited as:
- * 1. Right now an address of the stack is relative to load time
- * addresses what will cause an issue in case of load start address
- * isn't equal to linker start address.
- * 2. Addresses in stack are all load time relative which can be an
- * issue in case when load start address isn't equal to linker
- * start address.
- *
- * We can't return to the caller because the stack was reseted
- * and it may have stash some variable on the stack.
- * Jump to a brand new function as the stack was reseted
- */
+ if ( index != xen_index )
+ {
+ pgtbl[index].pte = 0;
+ break;
+ }
- switch_stack_and_jump((unsigned long)cpu0_boot_stack + STACK_SIZE,
- cont_after_mmu_is_enabled);
+ pgtbl = (pte_t *)LOAD_TO_LINK(pte_to_paddr(pgtbl[index]));
+ }
}
/*
diff --git a/xen/arch/riscv/riscv64/head.S b/xen/arch/riscv/riscv64/head.S
index ae194bb099..f4e24fc3df 100644
--- a/xen/arch/riscv/riscv64/head.S
+++ b/xen/arch/riscv/riscv64/head.S
@@ -39,6 +39,23 @@ ENTRY(start)
jal calc_phys_offset
mv s2, a0
+ jal setup_initial_pagetables
+
+ /* Calculate proper VA after jump from 1:1 mapping */
+ la t0, .L_primary_switched
+ sub t0, t0, s2
+
+ mv a0, t0
+ jal turn_on_mmu
+
+.L_primary_switched:
+ /*
+ * cpu0_boot_stack address is 1:1 mapping related so it should be
+ * recalculated after jump from 1:1 mapping world as 1:1 mapping
+ * will be removed soon in start_xen().
+ */
+ jal reset_stack
+
/* restore hart_id ( bootcpu_id ) and dtb address */
mv a0, s0
mv a1, s1
@@ -54,3 +71,18 @@ ENTRY(reset_stack)
ret
+ .section .text.ident, "ax", %progbits
+
+ENTRY(turn_on_mmu)
+ sfence.vma
+
+ li t0, RV_STAGE1_MODE
+ li t1, SATP_MODE_SHIFT
+ sll t0, t0, t1
+
+ la t2, stage1_pgtbl_root
+ srl t2, t2, PAGE_SHIFT
+ or t2, t2, t0
+ csrw CSR_SATP, t2
+
+ jr a0
diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
index dde8fb898b..6593f601c1 100644
--- a/xen/arch/riscv/setup.c
+++ b/xen/arch/riscv/setup.c
@@ -13,20 +13,10 @@ unsigned char __initdata cpu0_boot_stack[STACK_SIZE]
void __init noreturn start_xen(unsigned long bootcpu_id,
paddr_t dtb_addr)
{
- early_printk("Hello from C env\n");
-
- setup_initial_pagetables();
-
- enable_mmu();
-
- for ( ;; )
- asm volatile ("wfi");
+ remove_identity_mapping();
- unreachable();
-}
+ early_printk("Hello from C env\n");
-void __init noreturn cont_after_mmu_is_enabled(void)
-{
early_printk("All set up\n");
for ( ;; )
diff --git a/xen/arch/riscv/xen.lds.S b/xen/arch/riscv/xen.lds.S
index 9064852173..3fa7db3bf9 100644
--- a/xen/arch/riscv/xen.lds.S
+++ b/xen/arch/riscv/xen.lds.S
@@ -31,6 +31,11 @@ SECTIONS
*(.text.*)
#endif
+ . = ALIGN(IDENT_AREA_SIZE);
+ _ident_start = .;
+ *(.text.ident)
+ _ident_end = .;
+
*(.fixup)
*(.gnu.warning)
. = ALIGN(POINTER_ALIGN);
@@ -173,4 +178,10 @@ ASSERT(IS_ALIGNED(__bss_end, POINTER_ALIGN), "__bss_end is misaligned")
ASSERT(!SIZEOF(.got), ".got non-empty")
ASSERT(!SIZEOF(.got.plt), ".got.plt non-empty")
+/*
+ * Changing the size of Xen binary can require an update of
+ * PGTBL_INITIAL_COUNT.
+ */
ASSERT(_end - _start <= MB(2), "Xen too large for early-boot assumptions")
+
+ASSERT(_ident_end - _ident_start <= IDENT_AREA_SIZE, "identity region is too big");
--
2.41.0On 27.07.2023 15:38, Oleksii Kurochko wrote:
> --- a/xen/arch/riscv/riscv64/head.S
> +++ b/xen/arch/riscv/riscv64/head.S
> @@ -39,6 +39,23 @@ ENTRY(start)
> jal calc_phys_offset
> mv s2, a0
>
> + jal setup_initial_pagetables
> +
> + /* Calculate proper VA after jump from 1:1 mapping */
> + la t0, .L_primary_switched
> + sub t0, t0, s2
> +
> + mv a0, t0
> + jal turn_on_mmu
Any reason you don't do the calculation right in a0?
> @@ -54,3 +71,18 @@ ENTRY(reset_stack)
>
> ret
>
> + .section .text.ident, "ax", %progbits
> +
> +ENTRY(turn_on_mmu)
> + sfence.vma
> +
> + li t0, RV_STAGE1_MODE
> + li t1, SATP_MODE_SHIFT
> + sll t0, t0, t1
Can't the last two be folded to
slli t0, t0, SATP_MODE_SHIFT
(I don't recall what li's valid value range is, so I'm not sure if
li t0, RV_STAGE1_MODE << SATP_MODE_SHIFT
would be an option.)
Everything else looks good to me now, but will of course want a
maintainer looking over.
Jan
On Mon, 2023-07-31 at 16:07 +0200, Jan Beulich wrote: > On 27.07.2023 15:38, Oleksii Kurochko wrote: > > --- a/xen/arch/riscv/riscv64/head.S > > +++ b/xen/arch/riscv/riscv64/head.S > > @@ -39,6 +39,23 @@ ENTRY(start) > > jal calc_phys_offset > > mv s2, a0 > > > > + jal setup_initial_pagetables > > + > > + /* Calculate proper VA after jump from 1:1 mapping */ > > + la t0, .L_primary_switched > > + sub t0, t0, s2 > > + > > + mv a0, t0 > > + jal turn_on_mmu > > Any reason you don't do the calculation right in a0? Probably it was before. But you are right there is no any sense in using of t0 in the current code. I'll update that. Thanks. > > > @@ -54,3 +71,18 @@ ENTRY(reset_stack) > > > > ret > > > > + .section .text.ident, "ax", %progbits > > + > > +ENTRY(turn_on_mmu) > > + sfence.vma > > + > > + li t0, RV_STAGE1_MODE > > + li t1, SATP_MODE_SHIFT > > + sll t0, t0, t1 > > Can't the last two be folded to > > slli t0, t0, SATP_MODE_SHIFT > > (I don't recall what li's valid value range is, so I'm not sure if > > li t0, RV_STAGE1_MODE << SATP_MODE_SHIFT > > would be an option.) Both of options will work but I prefer to use SLLI as LI expands into a potentially long and inefficient shift-and-add sequence ( but in this case I think this is not so important ). > > Everything else looks good to me now, but will of course want a > maintainer looking over. Would it be better to send a new version now or wait for a response from other maintainers? ~ Oleksii
On 01.08.2023 10:50, Oleksii wrote: > On Mon, 2023-07-31 at 16:07 +0200, Jan Beulich wrote: >> Everything else looks good to me now, but will of course want a >> maintainer looking over. > Would it be better to send a new version now or wait for a response > from other maintainers? Hard to tell. Maybe send a new version in the hope that that's what then can go in. Jan
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