[v5,1/2] kvm: add support for guest physical bits

Commit Message

Gerd Hoffmann March 25, 2024, 2:47 p.m. UTC

Query kvm for supported guest physical address bits, in cpuid
function 80000008, eax[23:16].  Usually this is identical to host
physical address bits.  With NPT or EPT being used this might be
restricted to 48 (max 4-level paging address space size) even if
the host cpu supports more physical address bits.

When set pass this to the guest, using cpuid too.  Guest firmware
can use this to figure how big the usable guest physical address
space is, so PCI bar mapping are actually reachable.

Signed-off-by: Gerd Hoffmann <[e-mail]>
---
 target/i386/cpu.h         |  1 +
 target/i386/cpu.c         |  1 +
 target/i386/kvm/kvm-cpu.c | 31 ++++++++++++++++++++++++++++++-
 3 files changed, 32 insertions(+), 1 deletion(-)

Patch

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 6b0573807918..83e473584517 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -2026,6 +2026,7 @@  struct ArchCPU {
 
     /* Number of physical address bits supported */
     uint32_t phys_bits;
+    uint32_t guest_phys_bits;
 
     /* in order to simplify APIC support, we leave this pointer to the
        user */
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 33760a2ee163..3b7bd506baf1 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6570,6 +6570,7 @@  void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         if (env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) {
             /* 64 bit processor */
              *eax |= (cpu_x86_virtual_addr_width(env) << 8);
+             *eax |= (cpu->guest_phys_bits << 16);
         }
         *ebx = env->features[FEAT_8000_0008_EBX];
         if (cs->nr_cores * cs->nr_threads > 1) {
diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
index 9c791b7b0520..c5c24f6a8282 100644
--- a/target/i386/kvm/kvm-cpu.c
+++ b/target/i386/kvm/kvm-cpu.c
@@ -18,10 +18,33 @@ 
 #include "kvm_i386.h"
 #include "hw/core/accel-cpu.h"
 
+static void kvm_set_guest_phys_bits(CPUState *cs)
+{
+    X86CPU *cpu = X86_CPU(cs);
+    uint32_t eax, guest_phys_bits;
+
+    eax = kvm_arch_get_supported_cpuid(cs->kvm_state, 0x80000008, 0, R_EAX);
+    guest_phys_bits = (eax >> 16) & 0xff;
+    if (!guest_phys_bits) {
+        return;
+    }
+
+    if (cpu->guest_phys_bits == 0 ||
+        cpu->guest_phys_bits > guest_phys_bits) {
+        cpu->guest_phys_bits = guest_phys_bits;
+    }
+
+    if (cpu->host_phys_bits && cpu->host_phys_bits_limit &&
+        cpu->guest_phys_bits > cpu->host_phys_bits_limit) {
+        cpu->guest_phys_bits = cpu->host_phys_bits_limit;
+    }
+}
+
 static bool kvm_cpu_realizefn(CPUState *cs, Error **errp)
 {
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
+    bool ret;
 
     /*
      * The realize order is important, since x86_cpu_realize() checks if
@@ -50,7 +73,13 @@  static bool kvm_cpu_realizefn(CPUState *cs, Error **errp)
                                                    MSR_IA32_UCODE_REV);
         }
     }
-    return host_cpu_realizefn(cs, errp);
+    ret = host_cpu_realizefn(cs, errp);
+    if (!ret) {
+        return ret;
+    }
+
+    kvm_set_guest_phys_bits(cs);
+    return true;
 }
 
 static bool lmce_supported(void)