| Message ID | 20230919150108.1233582-1-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] x86/entry: Partially revert IST-exit checks | expand |
On 19.09.2023 17:01, Andrew Cooper wrote: > The patch adding check_ist_exit() neglected to consider reset_stack_and_jump() > leaving C and entering one of the Xen exit paths. The value in %r12 is stale, > and depending on compiler decisions may not be 0. And it may also not be zero that we would be looking for. I think this wants expressing differently. The value in %r12 simply doesn't survive, and this has at best little to do with compiler decisions. > This shows up in Gitlab CI for the Clang build: > > https://gitlab.com/xen-project/people/andyhhp/xen/-/jobs/5112783827 > > and in OSSTest for GCC 8: > > http://logs.test-lab.xenproject.org/osstest/logs/183045/test-amd64-amd64-xl-qemuu-debianhvm-amd64/serial-pinot0.log > > There's no straightforward way to reconstruct the IST-exit-ness on the > exit-to-guest path after a context switch. For now, we only need IST-exit on > the return-to-Xen path. > > Fixes: 21bdc25b05a0 ("x86/entry: Track the IST-ness of an entry for the exit paths") > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Code change itself: Reviewed-by: Jan Beulich <jbeulich@suse.com> Jan
diff --git a/xen/arch/x86/x86_64/compat/entry.S b/xen/arch/x86/x86_64/compat/entry.S index 7504bfb4f326..bd5abd8040bd 100644 --- a/xen/arch/x86/x86_64/compat/entry.S +++ b/xen/arch/x86/x86_64/compat/entry.S @@ -117,15 +117,8 @@ compat_process_trap: call compat_create_bounce_frame jmp compat_test_all_events -/* %rbx: struct vcpu, %r12: ist_exit, interrupts disabled */ +/* %rbx: struct vcpu, interrupts disabled */ ENTRY(compat_restore_all_guest) - -#ifdef CONFIG_DEBUG - mov %rsp, %rdi - mov %r12, %rsi - call check_ist_exit -#endif - ASSERT_INTERRUPTS_DISABLED mov $~(X86_EFLAGS_IOPL | X86_EFLAGS_VM), %r11d and UREGS_eflags(%rsp),%r11d diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S index 988ef6cbc628..5ca74f5f62b2 100644 --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -142,15 +142,8 @@ process_trap: .section .text.entry, "ax", @progbits -/* %rbx: struct vcpu, %r12: ist_exit, interrupts disabled */ +/* %rbx: struct vcpu, interrupts disabled */ restore_all_guest: - -#ifdef CONFIG_DEBUG - mov %rsp, %rdi - mov %r12, %rsi - call check_ist_exit -#endif - ASSERT_INTERRUPTS_DISABLED /* Stash guest SPEC_CTRL value while we can read struct vcpu. */
The patch adding check_ist_exit() neglected to consider reset_stack_and_jump() leaving C and entering one of the Xen exit paths. The value in %r12 is stale, and depending on compiler decisions may not be 0. This shows up in Gitlab CI for the Clang build: https://gitlab.com/xen-project/people/andyhhp/xen/-/jobs/5112783827 and in OSSTest for GCC 8: http://logs.test-lab.xenproject.org/osstest/logs/183045/test-amd64-amd64-xl-qemuu-debianhvm-amd64/serial-pinot0.log There's no straightforward way to reconstruct the IST-exit-ness on the exit-to-guest path after a context switch. For now, we only need IST-exit on the return-to-Xen path. Fixes: 21bdc25b05a0 ("x86/entry: Track the IST-ness of an entry for the exit paths") Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Jan Beulich <JBeulich@suse.com> CC: Roger Pau Monné <roger.pau@citrix.com> CC: Wei Liu <wl@xen.org> v2: * Rewrite. --- xen/arch/x86/x86_64/compat/entry.S | 9 +-------- xen/arch/x86/x86_64/entry.S | 9 +-------- 2 files changed, 2 insertions(+), 16 deletions(-) base-commit: ea36ac0de27c2a7c847a2a52c3e0f97a45864d81