[Qemu-devel] [PATCH] fix guest physical bits to match host, to go beyond 1TB guests

[Andrea Arcangeli <aarcange@redhat.com>]

Without this patch the guest physical bits are advertised as 40, not
44 or more depending on the hardware capability of the host.

That leads to guest kernel crashes with injection of page faults 9
(see oops: 0009) as bits above 40 in the guest pagetables are
considered reserved.

exregion-0206 [324572448] [17] ex_system_memory_space: System-Memory (width 32) R/W 0 Address=00000000FED00000
BUG: unable to handle kernel paging request at ffffc9006030e000
IP: [<ffffffff812fbb6f>] acpi_ex_system_memory_space_handler+0x23e/0x2cb
PGD e01f875067 PUD 1001f075067 PMD e0178d8067 PTE 80000000fed00173
Oops: 0009 [#1] SMP

(see PUD with bit >=40 set)

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Chegu Vinod <chegu_vinod@hp.com>
---
 target-i386/cpu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index e3f75a8..0e65673 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -2108,6 +2108,12 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
             /* 64 bit processor */
 /* XXX: The physical address space is limited to 42 bits in exec.c. */
             *eax = 0x00003028; /* 48 bits virtual, 40 bits physical */
+            if (kvm_enabled()) {
+                uint32_t _eax;
+                host_cpuid(0x80000000, 0, &_eax, NULL, NULL, NULL);
+                if (_eax >= 0x80000008)
+                    host_cpuid(0x80000008, 0, eax, NULL, NULL, NULL);
+            }
         } else {
             if (env->features[FEAT_1_EDX] & CPUID_PSE36) {
                 *eax = 0x00000024; /* 36 bits physical */