On 3/10/20 1:19 PM, Sean Christopherson wrote: > Has this been tested on the stable kernels? There's a recent bug report[*] > that suggests the 4.19 backport of this patch may be causing issues. I missed this went the stable patches went by... when backported to the older version of kvm_mmu_set_mmio_spte_mask() in the stable kernels (4.14 and 4.19), the call should have been: kvm_mmu_set_mmio_spte_mask(mask, mask) and not: kvm_mmu_set_mmio_spte_mask(mask, PT_WRITABLE_MASK | PT_USER_MASK); The call in the original upstream patch was: kvm_mmu_set_mmio_spte_mask(mask, mask, PT_WRITABLE_MASK | PT_USER_MASK); Tom > > [*] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D206795&data=02%7C01%7Cthomas.lendacky%40amd.com%7C559dd742543741e4bc7608d7c51fa1d5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637194611958586378&sdata=k%2F3WUFrqvibbf%2FEaCFgOIhUWMZ%2BqHjawmmy1GII7KgA%3D&reserved=0 > > > On Tue, Mar 10, 2020 at 01:41:18PM +0100, Greg Kroah-Hartman wrote: >> From: Tom Lendacky <thomas.lendacky@xxxxxxx> >> >> 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@xxxxxxxxx> >> Reviewed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> >> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx> >> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> >> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> >> >> --- >> arch/x86/kvm/svm.c | 43 +++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 43 insertions(+) >> >> --- a/arch/x86/kvm/svm.c >> +++ b/arch/x86/kvm/svm.c >> @@ -1088,6 +1088,47 @@ static int avic_ga_log_notifier(u32 ga_t >> return 0; >> } >> >> +/* >> + * 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, PT_WRITABLE_MASK | PT_USER_MASK); >> +} >> + >> static __init int svm_hardware_setup(void) >> { >> int cpu; >> @@ -1123,6 +1164,8 @@ static __init int svm_hardware_setup(voi >> kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE); >> } >> >> + svm_adjust_mmio_mask(); >> + >> for_each_possible_cpu(cpu) { >> r = svm_cpu_init(cpu); >> if (r) >> >>
