[PATCH] x86: cpu: Error out if memory exceeds addressable range

From: Nikunj A Dadhania <nikunj@amd.com>
To: <qemu-devel@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	<f4bug@amsat.org>, <Abraham.Shaju@amd.com>, <bharata@amd.com>,
	<nikunj@amd.com>
Subject: [PATCH] x86: cpu: Error out if memory exceeds addressable range
Date: Mon, 18 Jul 2022 13:47:34 +0530	[thread overview]
Message-ID: <20220718081734.135598-1-nikunj@amd.com> (raw)

Currently it is possible to start a guest with memory that is beyond
the addressable range of CPU and QEMU does not even warn about it.
The default phys_bits is 40 and can address 1TB. However it allows to
start a guest with greater than 1TB memory.

Prevent this by erroring out in such a scenario.

Reported-by: Shaju Abraham <Abraham.Shaju@amd.com>
Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
---
 target/i386/cpu.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 6a57ef13af..1afbdbac7d 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6376,6 +6376,7 @@ static void x86_cpu_hyperv_realize(X86CPU *cpu)
 
 static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
 {
+    MachineState *machine = MACHINE(qdev_get_machine());
     CPUState *cs = CPU(dev);
     X86CPU *cpu = X86_CPU(dev);
     X86CPUClass *xcc = X86_CPU_GET_CLASS(dev);
@@ -6541,6 +6542,15 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
         }
     }
 
+    if (BIT_ULL(cpu->phys_bits) < machine->maxram_size) {
+        error_setg(&local_err, "cannot setup guest memory: "
+                   "%s memory(%lu MiB) exceeds addressable limit(%llu MiB)",
+                   machine->maxram_size == machine->ram_size ? "" : "max",
+                   machine->maxram_size / MiB,
+                   BIT_ULL(cpu->phys_bits) / MiB);
+        goto out;
+    }
+
     /* Cache information initialization */
     if (!cpu->legacy_cache) {
         if (!xcc->model || !xcc->model->cpudef->cache_info) {
-- 
2.32.0


