[Xen-devel] [PATCH v3 for 4.13] x86/e820: fix 640k - 1M region reservation logic

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Converting a guest from PV to PV-in-PVH makes the guest to have 384k
less memory, which may confuse guest's balloon driver. This happens
because Xen unconditionally reserves 640k - 1M region in E820 despite
the fact that it's really a usable RAM in PVH boot mode.

Fix this by skipping region type change in virtualised environments,
trusting whatever memory map our hypervisor has provided.

Take a refactoring opportunity to introduce early_cpu_has_hypervisor().

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v2 --> v3:
- early_cpu_has_hypervisor() is added

CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/cpu/common.c   | 9 +++++++++
 xen/arch/x86/e820.c         | 6 ++++--
 xen/arch/x86/guest/xen.c    | 4 ++--
 xen/arch/x86/mm.c           | 2 +-
 xen/include/asm-x86/setup.h | 1 +
 5 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 6c6bd63301..adedb557df 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -274,6 +274,15 @@ static inline u32 phys_pkg_id(u32 cpuid_apic, int 
index_msb)
        return _phys_pkg_id(get_apic_id(), index_msb);
 }
 
+/*
+ * Sometimes it's too early to use cpu_has_hypervisor which is available only
+ * after early_cpu_init().
+ */
+bool __init early_cpu_has_hypervisor(void)
+{
+       return cpuid_ecx(1) & cpufeat_mask(X86_FEATURE_HYPERVISOR);
+}
+
 /* Do minimum CPU detection early.
    Fields really needed: vendor, cpuid_level, family, model, mask, cache 
alignment.
    The others are not touched to avoid unwanted side effects.
diff --git a/xen/arch/x86/e820.c b/xen/arch/x86/e820.c
index 8e8a2c4e1b..dbbe6cac0a 100644
--- a/xen/arch/x86/e820.c
+++ b/xen/arch/x86/e820.c
@@ -10,6 +10,7 @@
 #include <asm/mtrr.h>
 #include <asm/msr.h>
 #include <asm/guest.h>
+#include <asm/setup.h>
 
 /*
  * opt_mem: Limit maximum address of physical RAM.
@@ -318,9 +319,10 @@ static int __init copy_e820_map(struct e820entry * 
biosmap, unsigned int nr_map)
 
         /*
          * Some BIOSes claim RAM in the 640k - 1M region.
-         * Not right. Fix it up.
+         * Not right. Fix it up, but only when running on bare metal.
          */
-        if (type == E820_RAM) {
+        if ( !early_cpu_has_hypervisor() && type == E820_RAM )
+        {
             if (start < 0x100000ULL && end > 0xA0000ULL) {
                 if (start < 0xA0000ULL)
                     add_memory_region(start, 0xA0000ULL-start, type);
diff --git a/xen/arch/x86/guest/xen.c b/xen/arch/x86/guest/xen.c
index 7b7a5badab..48ea3224ea 100644
--- a/xen/arch/x86/guest/xen.c
+++ b/xen/arch/x86/guest/xen.c
@@ -31,6 +31,7 @@
 #include <asm/guest.h>
 #include <asm/msr.h>
 #include <asm/processor.h>
+#include <asm/setup.h>
 
 #include <public/arch-x86/cpuid.h>
 #include <public/hvm/params.h>
@@ -72,8 +73,7 @@ void __init probe_hypervisor(void)
     if ( xen_guest )
         return;
 
-    /* Too early to use cpu_has_hypervisor */
-    if ( !(cpuid_ecx(1) & cpufeat_mask(X86_FEATURE_HYPERVISOR)) )
+    if ( !early_cpu_has_hypervisor() )
         return;
 
     find_xen_leaves();
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 99816fc67c..df1641634c 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5943,7 +5943,7 @@ const struct platform_bad_page *__init 
get_platform_badpages(unsigned int *array
     case 0x000806e0: /* erratum KBL??? */
     case 0x000906e0: /* errata KBL??? / KBW114 / CFW103 */
         *array_size = (cpuid_eax(0) >= 7 &&
-                       !(cpuid_ecx(1) & cpufeat_mask(X86_FEATURE_HYPERVISOR)) 
&&
+                       !early_cpu_has_hypervisor() &&
                        (cpuid_count_ebx(7, 0) & 
cpufeat_mask(X86_FEATURE_HLE)));
         return &hle_bad_page;
     }
diff --git a/xen/include/asm-x86/setup.h b/xen/include/asm-x86/setup.h
index 861d46d6ac..ddd37907f1 100644
--- a/xen/include/asm-x86/setup.h
+++ b/xen/include/asm-x86/setup.h
@@ -16,6 +16,7 @@ extern unsigned long xenheap_initial_phys_start;
 
 void early_cpu_init(void);
 void early_time_init(void);
+bool early_cpu_has_hypervisor(void);
 
 void set_nr_cpu_ids(unsigned int max_cpus);
 
-- 
2.17.1


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