From: Tom Lendacky thomas.lendacky@amd.com
commit 52918ed5fcf05d97d257f4131e19479da18f5d16 upstream.
The KVM MMIO support uses bit 51 as the reserved bit to cause nested page faults when a guest performs MMIO. The AMD memory encryption support uses a CPUID function to define the encryption bit position. Given this, it is possible that these bits can conflict.
Use svm_hardware_setup() to override the MMIO mask if memory encryption support is enabled. Various checks are performed to ensure that the mask is properly defined and rsvd_bits() is used to generate the new mask (as was done prior to the change that necessitated this patch).
Fixes: 28a1f3ac1d0c ("kvm: x86: Set highest physical address bits in non-present/reserved SPTEs") Suggested-by: Sean Christopherson sean.j.christopherson@intel.com Reviewed-by: Sean Christopherson sean.j.christopherson@intel.com Signed-off-by: Tom Lendacky thomas.lendacky@amd.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/svm.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+)
--- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1298,6 +1298,47 @@ static void shrink_ple_window(struct kvm } }
+/* + * The default MMIO mask is a single bit (excluding the present bit), + * which could conflict with the memory encryption bit. Check for + * memory encryption support and override the default MMIO mask if + * memory encryption is enabled. + */ +static __init void svm_adjust_mmio_mask(void) +{ + unsigned int enc_bit, mask_bit; + u64 msr, mask; + + /* If there is no memory encryption support, use existing mask */ + if (cpuid_eax(0x80000000) < 0x8000001f) + return; + + /* If memory encryption is not enabled, use existing mask */ + rdmsrl(MSR_K8_SYSCFG, msr); + if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT)) + return; + + enc_bit = cpuid_ebx(0x8000001f) & 0x3f; + mask_bit = boot_cpu_data.x86_phys_bits; + + /* Increment the mask bit if it is the same as the encryption bit */ + if (enc_bit == mask_bit) + mask_bit++; + + /* + * If the mask bit location is below 52, then some bits above the + * physical addressing limit will always be reserved, so use the + * rsvd_bits() function to generate the mask. This mask, along with + * the present bit, will be used to generate a page fault with + * PFER.RSV = 1. + * + * If the mask bit location is 52 (or above), then clear the mask. + */ + mask = (mask_bit < 52) ? rsvd_bits(mask_bit, 51) | PT_PRESENT_MASK : 0; + + kvm_mmu_set_mmio_spte_mask(mask, mask, PT_WRITABLE_MASK | PT_USER_MASK); +} + static __init int svm_hardware_setup(void) { int cpu; @@ -1352,6 +1393,8 @@ static __init int svm_hardware_setup(voi } }
+ svm_adjust_mmio_mask(); + for_each_possible_cpu(cpu) { r = svm_cpu_init(cpu); if (r)