Re: [Qemu-devel][PATCH] x86/cpu: Use max host physical address if -cpu max option is applied

[Paolo Bonzini]

On 25/01/21 08:10, Nathan Chancellor wrote:
This patch as commit 5a140b255d ("x86/cpu: Use max host physical address
if -cpu max option is applied") prevents me from using '-cpu host' while
booting an i386_defconfig kernel.
$ qemu-system-i386 \
-append console=ttyS0 \
-cpu host \
-display none \
-enable-kvm \
-initrd rootfs.cpio \
-kernel bzImage \
-serial mon:stdio
qemu-system-i386: phys-bits should be between 32 and 36  (but is 48)

Am I expected to pass "-cpu host,host-phys-bits=false" now or did this
do something unexpected?

Yes, it's setting the LM bit for a 32-bit guest.

Does this work for you?

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 72a79e6019..70df57337f 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5081,6 +5081,11 @@ static uint64_t 
x86_cpu_get_supported_feature_word(FeatureWord w,
     } else {
         return ~0;
     }
+#ifdef TARGET_I386
+    if (wi->cpuid.eax = 0x80000001) {
+        r &= ~CPUID_EXT2_LM;
+    }
+#endif
     if (migratable_only) {
         r &= x86_cpu_get_migratable_flags(w);
     }


Paolo

Hi, Nathan,
Could you try Paolo's latest patch?

[PULL 03/31] x86/cpu: Use max host physical address if -cpu max option is 
applied

Hi Yang,

That is the version of the patch I tried, which has been pulled into the
master branch.

Cheers,
Nathan