[PATCH RFCv2 12/15] xen/arm: add Persistent Map (PMAP) infrastructure

[Julien Grall <julien@xxxxxxx>]

From: Wei Liu <wei.liu2@xxxxxxxxxx>

The basic idea is like Persistent Kernel Map (PKMAP) in Linux. We
pre-populate all the relevant page tables before the system is fully
set up.

We will need it on Arm in order to rework the arm64 version of
xenheap_setup_mappings() as we may need to use pages allocated from
the boot allocator before they are effectively mapped.

This infrastructure is not lock-protected therefore can only be used
before smpboot. After smpboot, map_domain_page() has to be used.

This is based on the x86 version [1] that was originally implemented
by Wei Liu.

Take the opportunity to switch the parameter attr from unsigned to
unsigned int.

[1] 
<e92da4ad6015b6089737fcccba3ec1d6424649a5.1588278317.git.hongyxia@xxxxxxxxxx>

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Signed-off-by: Hongyan Xia <hongyxia@xxxxxxxxxx>
[julien: Adapted for Arm]
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

---
    Changes in v2:
        - New patch

Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Wei Liu <wl@xxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Hongian Xia <hongyax@xxxxxxxxxx>

This is mostly a copy of the PMAP infrastructure currently discussed
on x86. The only difference is how the page-tables are updated.

I think we want to consider to provide a common infrastructure. But
I haven't done it yet to gather feedback on the overall series
first.
---
 xen/arch/arm/Makefile        |   1 +
 xen/arch/arm/mm.c            |   7 +--
 xen/arch/arm/pmap.c          | 101 +++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/config.h |   2 +
 xen/include/asm-arm/lpae.h   |   8 +++
 xen/include/asm-arm/pmap.h   |  10 ++++
 6 files changed, 123 insertions(+), 6 deletions(-)
 create mode 100644 xen/arch/arm/pmap.c
 create mode 100644 xen/include/asm-arm/pmap.h

diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
index ca75f1040dcc..2196ada24941 100644
--- a/xen/arch/arm/Makefile
+++ b/xen/arch/arm/Makefile
@@ -40,6 +40,7 @@ obj-y += percpu.o
 obj-y += platform.o
 obj-y += platform_hypercall.o
 obj-y += physdev.o
+obj-y += pmap.init.o
 obj-y += processor.o
 obj-y += psci.o
 obj-y += setup.o
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index d090fdfd5994..5e713b599611 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -288,12 +288,7 @@ void dump_hyp_walk(vaddr_t addr)
     dump_pt_walk(ttbr, addr, HYP_PT_ROOT_LEVEL, 1);
 }
 
-/*
- * Standard entry type that we'll use to build Xen's own pagetables.
- * We put the same permissions at every level, because they're ignored
- * by the walker in non-leaf entries.
- */
-static inline lpae_t mfn_to_xen_entry(mfn_t mfn, unsigned attr)
+lpae_t mfn_to_xen_entry(mfn_t mfn, unsigned int attr)
 {
     lpae_t e = (lpae_t) {
         .pt = {
diff --git a/xen/arch/arm/pmap.c b/xen/arch/arm/pmap.c
new file mode 100644
index 000000000000..702b1bde982d
--- /dev/null
+++ b/xen/arch/arm/pmap.c
@@ -0,0 +1,101 @@
+#include <xen/init.h>
+#include <xen/mm.h>
+
+#include <asm/bitops.h>
+#include <asm/flushtlb.h>
+#include <asm/pmap.h>
+
+/*
+ * To be able to use FIXMAP_PMAP_BEGIN.
+ * XXX: move fixmap definition in a separate header
+ */
+#include <xen/acpi.h>
+
+/*
+ * Simple mapping infrastructure to map / unmap pages in fixed map.
+ * This is used to set up the page table for mapcache, which is used
+ * by map domain page infrastructure.
+ *
+ * This structure is not protected by any locks, so it must not be used after
+ * smp bring-up.
+ */
+
+/* Bitmap to track which slot is used */
+static unsigned long __initdata inuse;
+
+/* XXX: Find an header to declare it */
+extern lpae_t xen_fixmap[LPAE_ENTRIES];
+
+void *__init pmap_map(mfn_t mfn)
+{
+    unsigned long flags;
+    unsigned int idx;
+    vaddr_t linear;
+    unsigned int slot;
+    lpae_t *entry, pte;
+
+    BUILD_BUG_ON(sizeof(inuse) * BITS_PER_LONG < NUM_FIX_PMAP);
+
+    ASSERT(system_state < SYS_STATE_smp_boot);
+
+    local_irq_save(flags);
+
+    idx = find_first_zero_bit(&inuse, NUM_FIX_PMAP);
+    if ( idx == NUM_FIX_PMAP )
+        panic("Out of PMAP slots\n");
+
+    __set_bit(idx, &inuse);
+
+    slot = idx + FIXMAP_PMAP_BEGIN;
+    ASSERT(slot >= FIXMAP_PMAP_BEGIN && slot <= FIXMAP_PMAP_END);
+
+    linear = FIXMAP_ADDR(slot);
+    /*
+     * We cannot use set_fixmap() here. We use PMAP when there is no direct 
map,
+     * so map_pages_to_xen() called by set_fixmap() needs to map pages on
+     * demand, which then calls pmap() again, resulting in a loop. Modify the
+     * PTEs directly instead. The same is true for pmap_unmap().
+     */
+    entry = &xen_fixmap[third_table_offset(linear)];
+
+    ASSERT(!lpae_is_valid(*entry));
+
+    pte = mfn_to_xen_entry(mfn, PAGE_HYPERVISOR_RW);
+    pte.pt.table = 1;
+    write_pte(entry, pte);
+
+    local_irq_restore(flags);
+
+    return (void *)linear;
+}
+
+void __init pmap_unmap(const void *p)
+{
+    unsigned long flags;
+    unsigned int idx;
+    lpae_t *entry;
+    lpae_t pte = { 0 };
+    unsigned int slot = third_table_offset((vaddr_t)p);
+
+    ASSERT(system_state < SYS_STATE_smp_boot);
+    ASSERT(slot >= FIXMAP_PMAP_BEGIN && slot <= FIXMAP_PMAP_END);
+
+    idx = slot - FIXMAP_PMAP_BEGIN;
+    local_irq_save(flags);
+
+    __clear_bit(idx, &inuse);
+    entry = &xen_fixmap[third_table_offset((vaddr_t)p)];
+    write_pte(entry, pte);
+    flush_xen_tlb_range_va_local((vaddr_t)p, PAGE_SIZE);
+
+    local_irq_restore(flags);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/asm-arm/config.h b/xen/include/asm-arm/config.h
index 85d4a510ce8a..35050855b6e1 100644
--- a/xen/include/asm-arm/config.h
+++ b/xen/include/asm-arm/config.h
@@ -180,6 +180,8 @@
 #define FIXMAP_MISC     1  /* Ephemeral mappings of hardware */
 #define FIXMAP_ACPI_BEGIN  2  /* Start mappings of ACPI tables */
 #define FIXMAP_ACPI_END    (FIXMAP_ACPI_BEGIN + NUM_FIXMAP_ACPI_PAGES - 1)  /* 
End mappings of ACPI tables */
+#define FIXMAP_PMAP_BEGIN (FIXMAP_ACPI_END + 1)
+#define FIXMAP_PMAP_END (FIXMAP_PMAP_BEGIN + NUM_FIX_PMAP - 1)
 
 #define NR_hypercalls 64
 
diff --git a/xen/include/asm-arm/lpae.h b/xen/include/asm-arm/lpae.h
index 310f5225e056..81fd482ab2ce 100644
--- a/xen/include/asm-arm/lpae.h
+++ b/xen/include/asm-arm/lpae.h
@@ -4,6 +4,7 @@
 #ifndef __ASSEMBLY__
 
 #include <xen/page-defs.h>
+#include <xen/mm-frame.h>
 
 /*
  * WARNING!  Unlike the x86 pagetable code, where l1 is the lowest level and
@@ -168,6 +169,13 @@ static inline bool lpae_is_superpage(lpae_t pte, unsigned 
int level)
         third_table_offset(addr)            \
     }
 
+/*
+ * Standard entry type that we'll use to build Xen's own pagetables.
+ * We put the same permissions at every level, because they're ignored
+ * by the walker in non-leaf entries.
+ */
+lpae_t mfn_to_xen_entry(mfn_t mfn, unsigned int attr);
+
 #endif /* __ASSEMBLY__ */
 
 /*
diff --git a/xen/include/asm-arm/pmap.h b/xen/include/asm-arm/pmap.h
new file mode 100644
index 000000000000..8e1dce93f8e4
--- /dev/null
+++ b/xen/include/asm-arm/pmap.h
@@ -0,0 +1,10 @@
+#ifndef __ASM_PMAP_H__
+#define __ARM_PMAP_H__
+
+/* Large enough for mapping 5 levels of page tables with some headroom */
+#define NUM_FIX_PMAP 8
+
+void *pmap_map(mfn_t mfn);
+void pmap_unmap(const void *p);
+
+#endif /* __ASM_PMAP_H__ */
-- 
2.17.1