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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v4 13/14] xen/arm64: mm: Rework switch_ttbr()
From: Julien Grall <jgrall@xxxxxxxxxx>
At the moment, switch_ttbr() is switching the TTBR whilst the MMU is
still on.
Switching TTBR is like replacing existing mappings with new ones. So
we need to follow the break-before-make sequence.
In this case, it means the MMU needs to be switched off while the
TTBR is updated. In order to disable the MMU, we need to first
jump to an identity mapping.
Rename switch_ttbr() to switch_ttbr_id() and create an helper on
top to temporary map the identity mapping and call switch_ttbr()
via the identity address.
switch_ttbr_id() is now reworked to temporarily turn off the MMU
before updating the TTBR.
We also need to make sure the helper switch_ttbr() is part of the
identity mapping. So move _end_boot past it.
The arm32 code will use a different approach. So this issue is for now
only resolved on arm64.
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
----
Changes in v4:
- Don't modify setup_pagetables() as we don't handle arm32.
- Move the clearing of the boot page tables in an earlier patch
- Fix the numbering
Changes in v2:
- Remove the arm32 changes. This will be addressed differently
- Re-instate the instruct cache flush. This is not strictly
necessary but kept it for safety.
- Use "dsb ish" rather than "dsb sy".
TODO:
* Handle the case where the runtime Xen is loaded at a different
position for cache coloring. This will be dealt separately.
---
xen/arch/arm/arm64/head.S | 50 +++++++++++++++++++++++------------
xen/arch/arm/arm64/mm.c | 30 +++++++++++++++++++++
xen/arch/arm/include/asm/mm.h | 2 ++
xen/arch/arm/mm.c | 2 --
4 files changed, 65 insertions(+), 19 deletions(-)
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 663f5813b12e..5efd442b24af 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -816,30 +816,46 @@ ENDPROC(fail)
* Switch TTBR
*
* x0 ttbr
- *
- * 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
- * changes to text */
- tlbi alle2 /* Flush hypervisor TLB */
- ic iallu /* Flush I-cache */
- dsb sy /* Ensure completion of TLB flush */
+ENTRY(switch_ttbr_id)
+ /* 1) Ensure any previous read/write have completed */
+ dsb ish
+ isb
+
+ /* 2) Turn off MMU */
+ mrs x1, SCTLR_EL2
+ bic x1, x1, #SCTLR_Axx_ELx_M
+ msr SCTLR_EL2, x1
+ isb
+
+ /*
+ * 3) Flush the TLBs.
+ * See asm/arm64/flushtlb.h for the explanation of the sequence.
+ */
+ dsb nshst
+ tlbi alle2
+ dsb nsh
+ isb
+
+ /* 4) Update the TTBR */
+ msr TTBR0_EL2, x0
isb
- msr TTBR0_EL2, x0
+ /*
+ * 5) Flush I-cache
+ * This should not be necessary but it is kept for safety.
+ */
+ ic iallu
+ isb
- isb /* Ensure synchronization with previous
- * changes to text */
- tlbi alle2 /* Flush hypervisor TLB */
- ic iallu /* Flush I-cache */
- dsb sy /* Ensure completion of TLB flush */
+ /* 6) Turn on the MMU */
+ mrs x1, SCTLR_EL2
+ orr x1, x1, #SCTLR_Axx_ELx_M /* Enable MMU */
+ msr SCTLR_EL2, x1
isb
ret
-ENDPROC(switch_ttbr)
+ENDPROC(switch_ttbr_id)
#ifdef CONFIG_EARLY_PRINTK
/*
diff --git a/xen/arch/arm/arm64/mm.c b/xen/arch/arm/arm64/mm.c
index 798ae93ad73c..2ede4e75ae33 100644
--- a/xen/arch/arm/arm64/mm.c
+++ b/xen/arch/arm/arm64/mm.c
@@ -120,6 +120,36 @@ void update_identity_mapping(bool enable)
BUG_ON(rc);
}
+extern void switch_ttbr_id(uint64_t ttbr);
+
+typedef void (switch_ttbr_fn)(uint64_t ttbr);
+
+void __init switch_ttbr(uint64_t ttbr)
+{
+ vaddr_t id_addr = virt_to_maddr(switch_ttbr_id);
+ switch_ttbr_fn *fn = (switch_ttbr_fn *)id_addr;
+ lpae_t pte;
+
+ /* Enable the identity mapping in the boot page tables */
+ update_identity_mapping(true);
+ /* Enable the identity mapping in the runtime page tables */
+ pte = pte_of_xenaddr((vaddr_t)switch_ttbr_id);
+ pte.pt.table = 1;
+ pte.pt.xn = 0;
+ pte.pt.ro = 1;
+ write_pte(&xen_third_id[third_table_offset(id_addr)], pte);
+
+ /* Switch TTBR */
+ fn(ttbr);
+
+ /*
+ * Disable the identity mapping in the runtime page tables.
+ * Note it is not necessary to disable it in the boot page tables
+ * because they are not going to be used by this CPU anymore.
+ */
+ update_identity_mapping(false);
+}
+
/*
* Local variables:
* mode: C
diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index 68adcac9fa8d..bff6923f3ea9 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -196,6 +196,8 @@ extern unsigned long total_pages;
extern void setup_pagetables(unsigned long boot_phys_offset);
/* Map FDT in boot pagetable */
extern void *early_fdt_map(paddr_t fdt_paddr);
+/* Switch to a new root page-tables */
+extern void switch_ttbr(uint64_t ttbr);
/* Remove early mappings */
extern void remove_early_mappings(void);
/* Allocate and initialise pagetables for a secondary CPU. Sets init_ttbr to
the
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 39e0d9e03c9c..b9c698088b25 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -476,8 +476,6 @@ static void xen_pt_enforce_wnx(void)
flush_xen_tlb_local();
}
-extern void switch_ttbr(uint64_t ttbr);
-
/* Clear a translation table and clean & invalidate the cache */
static void clear_table(void *table)
{
--
2.38.1
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