[1/4] better kvm detection

Commit Message

Gerd Hoffmann Nov. 21, 2022, 10:32 a.m. UTC

In case kvm emulates features of another hypervisor (for example hyperv)
two VMM CPUID blocks will be present, one for the emulated hypervisor
and one for kvm itself.

This patch makes seabios loop over the VMM CPUID blocks to make sure it
will properly detect kvm when multiple blocks are present.

Signed-off-by: Gerd Hoffmann <[e-mail]>
---
 src/fw/paravirt.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

Comments

David Woodhouse Jan. 20, 2023, 12:21 p.m. UTC | #1

On Mon, 2022-11-21 at 11:32 +0100, Gerd Hoffmann wrote:
> In case kvm emulates features of another hypervisor (for example hyperv)
> two VMM CPUID blocks will be present, one for the emulated hypervisor
> and one for kvm itself.

That isn't the case for emulating Xen on KVM, FWIW. Only for Hyper-V on
KVM (and also for Hyper-V on Xen).

Patch

diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
index fba4e52db684..c880cb10a1bc 100644
--- a/src/fw/paravirt.c
+++ b/src/fw/paravirt.c
@@ -56,20 +56,31 @@  inline int qemu_cfg_dma_enabled(void)
 
 static void kvm_detect(void)
 {
+    unsigned int i, kvmbase = 0, max = 0;
     unsigned int eax, ebx, ecx, edx;
     char signature[13];
 
-    cpuid(KVM_CPUID_SIGNATURE, &eax, &ebx, &ecx, &edx);
-    memcpy(signature + 0, &ebx, 4);
-    memcpy(signature + 4, &ecx, 4);
-    memcpy(signature + 8, &edx, 4);
-    signature[12] = 0;
+    for (i = KVM_CPUID_SIGNATURE;; i += 0x100) {
+        eax = 0;
+        cpuid(i, &eax, &ebx, &ecx, &edx);
+        if (eax < i)
+            break;
+        memcpy(signature + 0, &ebx, 4);
+        memcpy(signature + 4, &ecx, 4);
+        memcpy(signature + 8, &edx, 4);
+        signature[12] = 0;
+        dprintf(1, "cpuid 0x%x: eax %x, signature '%s'\n", i, eax, signature);
+        if (strcmp(signature, "KVMKVMKVM") == 0) {
+            kvmbase = i;
+            max = eax;
+        }
+    }
 
-    if (strcmp(signature, "KVMKVMKVM") == 0) {
+    if (kvmbase) {
         dprintf(1, "Running on KVM\n");
         PlatformRunningOn |= PF_KVM;
-        if (eax >= KVM_CPUID_SIGNATURE + 0x10) {
-            cpuid(KVM_CPUID_SIGNATURE + 0x10, &eax, &ebx, &ecx, &edx);
+        if (max >= kvmbase + 0x10) {
+            cpuid(kvmbase + 0x10, &eax, &ebx, &ecx, &edx);
             dprintf(1, "kvm: have invtsc, freq %u kHz\n", eax);
             tsctimer_setfreq(eax, "invtsc");
         }