From d24df8ecf9b6f81029f520ae7158a8670a28d70b Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Tue, 9 Feb 2021 18:33:34 -0800 Subject: [PATCH] x86/fault: Skip the AMD erratum #91 workaround on unaffected CPUs MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit According to the Revision Guide for AMD Athlon™ 64 and AMD Opteron™ Processors, only early revisions of family 0xF are affected. This will avoid unnecessarily fetching instruction bytes before sending SIGSEGV to user programs. Signed-off-by: Andy Lutomirski Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/477173b7784bc28afb3e53d76ae5ef143917e8dd.1612924255.git.luto@kernel.org --- arch/x86/mm/fault.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 441c3e9b8971..818902b08c52 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -106,6 +106,15 @@ check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, } } +static bool is_amd_k8_pre_npt(void) +{ + struct cpuinfo_x86 *c = &boot_cpu_data; + + return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) && + c->x86_vendor == X86_VENDOR_AMD && + c->x86 == 0xf && c->x86_model < 0x40); +} + static int is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) { @@ -113,6 +122,10 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) unsigned char *instr; int prefetch = 0; + /* Erratum #91 affects AMD K8, pre-NPT CPUs */ + if (!is_amd_k8_pre_npt()) + return 0; + /* * If it was a exec (instruction fetch) fault on NX page, then * do not ignore the fault: -- 2.11.0