On March 24, 2026 4:08:56 AM PDT, David Laight <[email protected]> wrote: >On Fri, 20 Mar 2026 14:33:01 +0800 >Yi Lai <[email protected]> wrote: > >> The existing 'sysret_rip' selftest asserts that 'regs->r11 == >> regs->flags'. This check relies on the behavior of the SYSCALL >> instruction on legacy x86_64, which saves 'RFLAGS' into 'R11'. >> >> However, on systems with FRED (Flexible Return and Event Delivery) >> enabled, instead of using registers, all state is saved onto the stack. >> Consequently, 'R11' retains its userspace value, causing the assertion >> to fail. >> >> Fix this by detecting FRED support via CPUID (Leaf 0x7, Subleaf 0x1, EAX >> bit 17) and skipping the register assertion if FRED is present. > >For the selftest can't you just allow for R11 being unchanged? >That would be much simpler. >It isn't as though the test is doing much more than checking that >R11 is corrupted by being overwritten by EFLAGS. > > David > >> >> Signed-off-by: Yi Lai <[email protected]> >> --- >> tools/testing/selftests/x86/sysret_rip.c | 16 +++++++++++++--- >> 1 file changed, 13 insertions(+), 3 deletions(-) >> >> diff --git a/tools/testing/selftests/x86/sysret_rip.c >> b/tools/testing/selftests/x86/sysret_rip.c >> index 2e423a335e1c..0228d6174d5b 100644 >> --- a/tools/testing/selftests/x86/sysret_rip.c >> +++ b/tools/testing/selftests/x86/sysret_rip.c >> @@ -21,6 +21,7 @@ >> #include <sys/user.h> >> #include <sys/mman.h> >> #include <assert.h> >> +#include <cpuid.h> >> >> #include "helpers.h" >> >> @@ -64,9 +65,18 @@ static void sigusr1(int sig, siginfo_t *info, void >> *ctx_void) >> ctx->uc_mcontext.gregs[REG_RIP] = rip; >> ctx->uc_mcontext.gregs[REG_RCX] = rip; >> >> - /* R11 and EFLAGS should already match. */ >> - assert(ctx->uc_mcontext.gregs[REG_EFL] == >> - ctx->uc_mcontext.gregs[REG_R11]); >> + /* >> + * SYSCALL works differently on FRED, it does not save RIP and RFLAGS >> + * to RCX and R11. >> + */ >> + unsigned int eax, ebx, ecx, edx; >> + >> + __cpuid_count(0x7, 0x1, eax, ebx, ecx, edx); >> + if (!(eax & (1 << 17))) { >> + /* R11 and EFLAGS should already match. */ >> + assert(ctx->uc_mcontext.gregs[REG_EFL] == >> + ctx->uc_mcontext.gregs[REG_R11]); >> + } >> >> sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND); >> } >
I thought we already made it do that a while ago...
