KVM: x86: Move shadow_phys_bits into "kvm_host", as "maxphyaddr"

Move shadow_phys_bits into "struct kvm_host_values", i.e. into KVM's
global "kvm_host" variable, so that it is automatically exported for use
in vendor modules.  Rename the variable/field to maxphyaddr to more
clearly capture what value it holds, now that it's used outside of the
MMU (and because the "shadow" part is more than a bit misleading as the
variable is not at all unique to shadow paging).

Recomputing the raw/true host.MAXPHYADDR on every use can be subtly
expensive, e.g. it will incur a VM-Exit on the CPUID if KVM is running as
a nested hypervisor.  Vendor code already has access to the information,
e.g. by directly doing CPUID or by invoking kvm_get_shadow_phys_bits(), so
there's no tangible benefit to making it MMU-only.

Link: https://lore.kernel.org/r/20240423221521.2923759-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index db4bc6f6c5a0..9ee81c17a2d5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8389,18 +8389,16 @@ static void __init vmx_setup_me_spte_mask(void)
 	u64 me_mask = 0;
 
 	/*
-	 * kvm_get_shadow_phys_bits() returns shadow_phys_bits.  Use
-	 * the former to avoid exposing shadow_phys_bits.
-	 *
 	 * On pre-MKTME system, boot_cpu_data.x86_phys_bits equals to
-	 * shadow_phys_bits.  On MKTME and/or TDX capable systems,
+	 * kvm_host.maxphyaddr.  On MKTME and/or TDX capable systems,
 	 * boot_cpu_data.x86_phys_bits holds the actual physical address
-	 * w/o the KeyID bits, and shadow_phys_bits equals to MAXPHYADDR
-	 * reported by CPUID.  Those bits between are KeyID bits.
+	 * w/o the KeyID bits, and kvm_host.maxphyaddr equals to
+	 * MAXPHYADDR reported by CPUID.  Those bits between are KeyID bits.
 	 */
-	if (boot_cpu_data.x86_phys_bits != kvm_get_shadow_phys_bits())
+	if (boot_cpu_data.x86_phys_bits != kvm_host.maxphyaddr)
 		me_mask = rsvd_bits(boot_cpu_data.x86_phys_bits,
-			kvm_get_shadow_phys_bits() - 1);
+				    kvm_host.maxphyaddr - 1);
+
 	/*
 	 * Unlike SME, host kernel doesn't support setting up any
 	 * MKTME KeyID on Intel platforms.  No memory encryption