[PATCH RFCv2 3/4] i386/pc: warn if phys-bits is too low

[Joao Martins]

Default phys-bits on Qemu is TCG_PHYS_BITS (40) which is enough
to address 1Tb (0xff ffff ffff). On AMD platforms, if a
ram-above-4g relocation happens and the CPU wasn't configured
with a big enough phys-bits, warn the user. There isn't a
catastrophic failure exactly, the guest will still boot, but
most likely won't be able to use more than ~4G of RAM.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 hw/i386/pc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index b060aedd38f3..f8712eb8427e 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -842,6 +842,7 @@ static void relocate_4g(MachineState *machine, 
PCMachineState *pcms)
     X86MachineState *x86ms = X86_MACHINE(pcms);
     ram_addr_t device_mem_size = 0;
     uint32_t eax, vendor[3];
+    hwaddr maxphysaddr;
 
     host_cpuid(0x0, 0, &eax, &vendor[0], &vendor[2], &vendor[1]);
     if (!IS_AMD_VENDOR(vendor)) {
@@ -858,6 +859,12 @@ static void relocate_4g(MachineState *machine, 
PCMachineState *pcms)
         return;
     }
 
+    maxphysaddr = ((hwaddr)1 << X86_CPU(first_cpu)->phys_bits) - 1;
+    if (maxphysaddr < AMD_ABOVE_1TB_START)
+        warn_report("Relocated RAM above 4G to start at %lu "
+                    "phys-bits too low (%u)",
+                    AMD_ABOVE_1TB_START, X86_CPU(first_cpu)->phys_bits);
+
     x86ms->above_4g_mem_start = AMD_ABOVE_1TB_START;
 }
 
-- 
2.17.2