6.9-stable review patch. If anyone has any objections, please let me know.
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From: Gerd Hoffmann kraxel@redhat.com
commit 6f5c9600621b4efb5c61b482d767432eb1ad3a9c upstream.
Drop KVM's propagation of GuestPhysBits (CPUID leaf 80000008, EAX[23:16]) to HostPhysBits (same leaf, EAX[7:0]) when advertising the address widths to userspace via KVM_GET_SUPPORTED_CPUID.
Per AMD, GuestPhysBits is intended for software use, and physical CPUs do not set that field. I.e. GuestPhysBits will be non-zero if and only if KVM is running as a nested hypervisor, and in that case, GuestPhysBits is NOT guaranteed to capture the CPU's effective MAXPHYADDR when running with TDP enabled.
E.g. KVM will soon use GuestPhysBits to communicate the CPU's maximum *addressable* guest physical address, which would result in KVM under- reporting PhysBits when running as an L1 on a CPU with MAXPHYADDR=52, but without 5-level paging.
Signed-off-by: Gerd Hoffmann kraxel@redhat.com Cc: stable@vger.kernel.org Reviewed-by: Xiaoyao Li xiaoyao.li@intel.com Link: https://lore.kernel.org/r/20240313125844.912415-2-kraxel@redhat.com [sean: rewrite changelog with --verbose, Cc stable@] Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/cpuid.c | 21 ++++++++++----------- 1 file changed, 10 insertions(+), 11 deletions(-)
--- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -1232,9 +1232,8 @@ static inline int __do_cpuid_func(struct entry->eax = entry->ebx = entry->ecx = 0; break; case 0x80000008: { - unsigned g_phys_as = (entry->eax >> 16) & 0xff; - unsigned virt_as = max((entry->eax >> 8) & 0xff, 48U); - unsigned phys_as = entry->eax & 0xff; + unsigned int virt_as = max((entry->eax >> 8) & 0xff, 48U); + unsigned int phys_as;
/* * If TDP (NPT) is disabled use the adjusted host MAXPHYADDR as @@ -1242,16 +1241,16 @@ static inline int __do_cpuid_func(struct * reductions in MAXPHYADDR for memory encryption affect shadow * paging, too. * - * If TDP is enabled but an explicit guest MAXPHYADDR is not - * provided, use the raw bare metal MAXPHYADDR as reductions to - * the HPAs do not affect GPAs. + * If TDP is enabled, use the raw bare metal MAXPHYADDR as + * reductions to the HPAs do not affect GPAs. */ - if (!tdp_enabled) - g_phys_as = boot_cpu_data.x86_phys_bits; - else if (!g_phys_as) - g_phys_as = phys_as; + if (!tdp_enabled) { + phys_as = boot_cpu_data.x86_phys_bits; + } else { + phys_as = entry->eax & 0xff; + }
- entry->eax = g_phys_as | (virt_as << 8); + entry->eax = phys_as | (virt_as << 8); entry->ecx &= ~(GENMASK(31, 16) | GENMASK(11, 8)); entry->edx = 0; cpuid_entry_override(entry, CPUID_8000_0008_EBX);