4.18-stable review patch. If anyone has any objections, please let me know.
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From: Paolo Bonzini pbonzini@redhat.com
To mitigate the L1 Terminal Fault vulnerability it's required to flush L1D on VMENTER to prevent rogue guests from snooping host memory.
CPUs will have a new control MSR via a microcode update to flush L1D with a single MSR write, but in the absence of microcode a fallback to a software based flush algorithm is required.
Add a software flush loop which is based on code from Intel.
[ tglx: Split out from combo patch ] [ bpetkov: Polish the asm code ]
Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/vmx.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 66 insertions(+), 5 deletions(-)
--- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -9599,6 +9599,46 @@ static int vmx_handle_exit(struct kvm_vc } }
+/* + * Software based L1D cache flush which is used when microcode providing + * the cache control MSR is not loaded. + * + * The L1D cache is 32 KiB on Nehalem and later microarchitectures, but to + * flush it is required to read in 64 KiB because the replacement algorithm + * is not exactly LRU. This could be sized at runtime via topology + * information but as all relevant affected CPUs have 32KiB L1D cache size + * there is no point in doing so. + */ +#define L1D_CACHE_ORDER 4 +static void *vmx_l1d_flush_pages; + +static void __maybe_unused vmx_l1d_flush(void) +{ + int size = PAGE_SIZE << L1D_CACHE_ORDER; + + asm volatile( + /* First ensure the pages are in the TLB */ + "xorl %%eax, %%eax\n" + ".Lpopulate_tlb:\n\t" + "movzbl (%[empty_zp], %%" _ASM_AX "), %%ecx\n\t" + "addl $4096, %%eax\n\t" + "cmpl %%eax, %[size]\n\t" + "jne .Lpopulate_tlb\n\t" + "xorl %%eax, %%eax\n\t" + "cpuid\n\t" + /* Now fill the cache */ + "xorl %%eax, %%eax\n" + ".Lfill_cache:\n" + "movzbl (%[empty_zp], %%" _ASM_AX "), %%ecx\n\t" + "addl $64, %%eax\n\t" + "cmpl %%eax, %[size]\n\t" + "jne .Lfill_cache\n\t" + "lfence\n" + :: [empty_zp] "r" (vmx_l1d_flush_pages), + [size] "r" (size) + : "eax", "ebx", "ecx", "edx"); +} + static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr) { struct vmcs12 *vmcs12 = get_vmcs12(vcpu); @@ -13198,13 +13238,29 @@ static struct kvm_x86_ops vmx_x86_ops __ .enable_smi_window = enable_smi_window, };
-static void __init vmx_setup_l1d_flush(void) +static int __init vmx_setup_l1d_flush(void) { + struct page *page; + if (vmentry_l1d_flush == VMENTER_L1D_FLUSH_NEVER || !boot_cpu_has_bug(X86_BUG_L1TF)) - return; + return 0; + + page = alloc_pages(GFP_KERNEL, L1D_CACHE_ORDER); + if (!page) + return -ENOMEM;
+ vmx_l1d_flush_pages = page_address(page); static_branch_enable(&vmx_l1d_should_flush); + return 0; +} + +static void vmx_free_l1d_flush_pages(void) +{ + if (vmx_l1d_flush_pages) { + free_pages((unsigned long)vmx_l1d_flush_pages, L1D_CACHE_ORDER); + vmx_l1d_flush_pages = NULL; + } }
static int __init vmx_init(void) @@ -13240,12 +13296,16 @@ static int __init vmx_init(void) } #endif
- vmx_setup_l1d_flush(); + r = vmx_setup_l1d_flush(); + if (r) + return r;
r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx), - __alignof__(struct vcpu_vmx), THIS_MODULE); - if (r) + __alignof__(struct vcpu_vmx), THIS_MODULE); + if (r) { + vmx_free_l1d_flush_pages(); return r; + }
#ifdef CONFIG_KEXEC_CORE rcu_assign_pointer(crash_vmclear_loaded_vmcss, @@ -13287,6 +13347,7 @@ static void __exit vmx_exit(void) static_branch_disable(&enable_evmcs); } #endif + vmx_free_l1d_flush_pages(); }
module_init(vmx_init)