[PATCH 08/16] x86: add Persistent Map (PMAP) infrastructure

[Hongyan Xia <hx242@xen.org>]

From: Wei Liu <wei.liu2@citrix.com>

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

It is needed to bootstrap map domain page infrastructure -- we need
some way to map pages to set up the mapcache without a direct map.

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

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Hongyan Xia <hongyxia@amazon.com>
---
 xen/arch/x86/Makefile        |  1 +
 xen/arch/x86/pmap.c          | 87 ++++++++++++++++++++++++++++++++++++
 xen/include/asm-x86/fixmap.h |  3 ++
 xen/include/asm-x86/pmap.h   | 10 +++++
 4 files changed, 101 insertions(+)
 create mode 100644 xen/arch/x86/pmap.c
 create mode 100644 xen/include/asm-x86/pmap.h

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 44137d919b..c8e565867b 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -52,6 +52,7 @@ obj-y += pci.o
 obj-y += percpu.o
 obj-y += physdev.o x86_64/physdev.o
 obj-y += platform_hypercall.o x86_64/platform_hypercall.o
+obj-bin-y += pmap.init.o
 obj-y += psr.o
 obj-y += setup.o
 obj-y += shutdown.o
diff --git a/xen/arch/x86/pmap.c b/xen/arch/x86/pmap.c
new file mode 100644
index 0000000000..44d02ece89
--- /dev/null
+++ b/xen/arch/x86/pmap.c
@@ -0,0 +1,87 @@
+#include <xen/init.h>
+#include <xen/mm.h>
+#include <xen/spinlock.h>
+
+#include <asm/bitops.h>
+#include <asm/fixmap.h>
+#include <asm/flushtlb.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;
+
+void *__init pmap_map(mfn_t mfn)
+{
+    unsigned long flags;
+    unsigned int idx;
+    void *linear = NULL;
+    enum fixed_addresses slot;
+    l1_pgentry_t *pl1e;
+
+    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 + FIX_PMAP_BEGIN;
+    ASSERT(slot >= FIX_PMAP_BEGIN && slot <= FIX_PMAP_END);
+
+    linear = fix_to_virt(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().
+     */
+    pl1e = &l1_fixmap[l1_table_offset((unsigned long)linear)];
+    l1e_write_atomic(pl1e, l1e_from_mfn(mfn, PAGE_HYPERVISOR));
+
+    local_irq_restore(flags);
+
+    return linear;
+}
+
+void __init pmap_unmap(void *p)
+{
+    unsigned long flags;
+    unsigned int idx;
+    l1_pgentry_t *pl1e;
+    enum fixed_addresses slot = __virt_to_fix((unsigned long)p);
+
+    ASSERT(system_state < SYS_STATE_smp_boot);
+    ASSERT(slot >= FIX_PMAP_BEGIN && slot <= FIX_PMAP_END);
+
+    idx = slot - FIX_PMAP_BEGIN;
+    local_irq_save(flags);
+
+    __clear_bit(idx, &inuse);
+    pl1e = &l1_fixmap[l1_table_offset((unsigned long)p)];
+    l1e_write_atomic(pl1e, l1e_empty());
+    flush_tlb_one_local(p);
+
+    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-x86/fixmap.h b/xen/include/asm-x86/fixmap.h
index 8330097a74..000f3b3375 100644
--- a/xen/include/asm-x86/fixmap.h
+++ b/xen/include/asm-x86/fixmap.h
@@ -24,6 +24,7 @@
 #include <xen/kexec.h>
 #include <asm/apicdef.h>
 #include <asm/msi.h>
+#include <asm/pmap.h>
 #include <acpi/apei.h>
 
 /*
@@ -49,6 +50,8 @@ enum fixed_addresses {
     FIX_XEN_SHARED_INFO,
 #endif /* CONFIG_XEN_GUEST */
     /* Everything else should go further down. */
+    FIX_PMAP_BEGIN,
+    FIX_PMAP_END = FIX_PMAP_BEGIN + NUM_FIX_PMAP - 1,
     FIX_APIC_BASE,
     FIX_IO_APIC_BASE_0,
     FIX_IO_APIC_BASE_END = FIX_IO_APIC_BASE_0 + MAX_IO_APICS-1,
diff --git a/xen/include/asm-x86/pmap.h b/xen/include/asm-x86/pmap.h
new file mode 100644
index 0000000000..790cd71fb3
--- /dev/null
+++ b/xen/include/asm-x86/pmap.h
@@ -0,0 +1,10 @@
+#ifndef __X86_PMAP_H__
+#define __X86_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(void *p);
+
+#endif	/* __X86_PMAP_H__ */
-- 
2.24.1.AMZN