xen/arm: add Persistent Map (PMAP) infrastructure

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.

The PMAP infrastructure is implemented in common code with some
arch helpers to set/clear the page-table entries and convertion
between a fixmap slot to a virtual address...

As mfn_to_xen_entry() now needs to be exported, take the opportunity
to swich the parameter attr from unsigned to unsigned int.

[1] <e92da4ad6015b6089737fcccba3ec1d6424649a5.1588278317.git.hongyxia@amazon.com>

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Hongyan Xia <hongyxia@amazon.com>
[julien: Adapted for Arm]
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Tested-by: Luca Fancellu <luca.fancellu@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/Kconfig

@@ -14,6 +14,7 @@ config ARM
 	select HAS_DEVICE_TREE
 	select HAS_PASSTHROUGH
 	select HAS_PDX
+	select HAS_PMAP
 	select IOMMU_FORCE_PT_SHARE
 
 config ARCH_DEFCONFIG

xen/arch/arm/include/asm/fixmap.h

@@ -5,20 +5,44 @@
 #define __ASM_FIXMAP_H
 
 #include <xen/acpi.h>
+#include <xen/pmap.h>
 
 /* Fixmap slots */
 #define FIXMAP_CONSOLE  0  /* The primary UART */
 #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) /* Start of PMAP */
+#define FIXMAP_PMAP_END (FIXMAP_PMAP_BEGIN + NUM_FIX_PMAP - 1) /* End of PMAP */
+
+#define FIXMAP_LAST FIXMAP_PMAP_END
+
+#define FIXADDR_START FIXMAP_ADDR(0)
+#define FIXADDR_TOP FIXMAP_ADDR(FIXMAP_LAST)
 
 #ifndef __ASSEMBLY__
 
+/*
+ * Direct access to xen_fixmap[] should only happen when {set,
+ * clear}_fixmap() is unusable (e.g. where we would end up to
+ * recursively call the helpers).
+ */
+extern lpae_t xen_fixmap[XEN_PT_LPAE_ENTRIES];
+
 /* Map a page in a fixmap entry */
 extern void set_fixmap(unsigned map, mfn_t mfn, unsigned attributes);
 /* Remove a mapping from a fixmap entry */
 extern void clear_fixmap(unsigned map);
 
+#define fix_to_virt(slot) ((void *)FIXMAP_ADDR(slot))
+
+static inline unsigned int virt_to_fix(vaddr_t vaddr)
+{
+    BUG_ON(vaddr >= FIXADDR_TOP || vaddr < FIXADDR_START);
+
+    return ((vaddr - FIXADDR_START) >> PAGE_SHIFT);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __ASM_FIXMAP_H */

xen/arch/arm/include/asm/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__ */
 
 /*

xen/arch/arm/include/asm/pmap.h

@@ -0,0 +1,29 @@
+#ifndef __ASM_PMAP_H__
+#define __ASM_PMAP_H__
+
+#include <xen/mm.h>
+
+#include <asm/fixmap.h>
+
+static inline void arch_pmap_map(unsigned int slot, mfn_t mfn)
+{
+    lpae_t *entry = &xen_fixmap[slot];
+    lpae_t pte;
+
+    ASSERT(!lpae_is_valid(*entry));
+
+    pte = mfn_to_xen_entry(mfn, PAGE_HYPERVISOR_RW);
+    pte.pt.table = 1;
+    write_pte(entry, pte);
+}
+
+static inline void arch_pmap_unmap(unsigned int slot)
+{
+    lpae_t pte = {};
+
+    write_pte(&xen_fixmap[slot], pte);
+
+    flush_xen_tlb_range_va_local(FIXMAP_ADDR(slot), PAGE_SIZE);
+}
+
+#endif /* __ASM_PMAP_H__ */

xen/arch/arm/mm.c

@@ -305,12 +305,7 @@ 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 = {

xen/common/Kconfig

@@ -49,6 +49,9 @@ config HAS_KEXEC
 config HAS_PDX
 	bool
 
+config HAS_PMAP
+	bool
+
 config HAS_SCHED_GRANULARITY
 	bool
 

xen/common/Makefile

@@ -29,6 +29,7 @@ obj-y += notifier.o
 obj-y += page_alloc.o
 obj-$(CONFIG_HAS_PDX) += pdx.o
 obj-$(CONFIG_PERF_COUNTERS) += perfc.o
+obj-bin-$(CONFIG_HAS_PMAP) += pmap.init.o
 obj-y += preempt.o
 obj-y += random.o
 obj-y += rangeset.o

xen/common/pmap.c

@@ -0,0 +1,72 @@
+#include <xen/bitops.h>
+#include <xen/init.h>
+#include <xen/irq.h>
+#include <xen/pmap.h>
+
+#include <asm/pmap.h>
+#include <asm/fixmap.h>
+
+/*
+ * Simple mapping infrastructure to map / unmap pages in fixed map.
+ * This is used to set the page table before the map domain page infrastructure
+ * is initialized.
+ *
+ * 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 __initdata DECLARE_BITMAP(inuse, NUM_FIX_PMAP);
+
+void *__init pmap_map(mfn_t mfn)
+{
+    unsigned int idx;
+    unsigned int slot;
+
+    ASSERT(system_state < SYS_STATE_smp_boot);
+    ASSERT(!in_irq());
+
+    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);
+
+    /*
+     * We cannot use set_fixmap() here. We use PMAP when the domain map
+     * page infrastructure is not yet initialized, 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().
+     */
+    arch_pmap_map(slot, mfn);
+
+    return fix_to_virt(slot);
+}
+
+void __init pmap_unmap(const void *p)
+{
+    unsigned int idx;
+    unsigned int slot = virt_to_fix((unsigned long)p);
+
+    ASSERT(system_state < SYS_STATE_smp_boot);
+    ASSERT(slot >= FIXMAP_PMAP_BEGIN && slot <= FIXMAP_PMAP_END);
+    ASSERT(!in_irq());
+
+    idx = slot - FIXMAP_PMAP_BEGIN;
+
+    __clear_bit(idx, inuse);
+    arch_pmap_unmap(slot);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */

xen/include/xen/pmap.h

@@ -0,0 +1,16 @@
+#ifndef __XEN_PMAP_H__
+#define __XEN_PMAP_H__
+
+/* Large enough for mapping 5 levels of page tables with some headroom */
+#define NUM_FIX_PMAP 8
+
+#ifndef __ASSEMBLY__
+
+#include <xen/mm-frame.h>
+
+void *pmap_map(mfn_t mfn);
+void pmap_unmap(const void *p);
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __XEN_PMAP_H__ */