On Wed, Oct 15, 2025 at 04:32:05PM -0500, Andy Chiu wrote: > On Wed, Oct 15, 2025 at 3:18 PM Andy Chiu <[email protected]> wrote: > > > > On Tue, Oct 7, 2025 at 6:58 AM Sergey Matyukevich <[email protected]> > > wrote: > > > > > > When ptrace updates vector CSR registers for a traced process, the > > > changes may not be immediately visible to the next ptrace operations > > > due to vector context switch optimizations. > > > > > > The function 'riscv_v_vstate_save' saves context only if mstatus.VS is > > > 'dirty'. However mstatus.VS of the traced process context may remain > > > 'clean' between two breakpoints, if no vector instructions were executed > > > between those two breakpoints. In this case the vector context will not > > > be saved at the second breakpoint. As a result, the second ptrace may > > > read stale vector CSR values. > > > > IIUC, the second ptrace should not get the stale vector CSR values. > > The second riscv_vr_get() should be reading from the context memory > > (vstate), which is updated from the last riscv_vr_set(). The user's > > vstate should remain the same since last riscv_vr_set(). Could you > > explain more on how this bug is observed and why only CSRs are > > affected but not v-regs as well? > > From looking into your test, I can see that you were trying to set an > invalid configuration to Vetor CSRs and expect vill to be reflected > upon next read. Yes, this is not happening on the current > implementation as it was not expecting invalid input from the user, > which should be taken into consideration. Thanks for spotting the > case! > > According to the spec, "The use of vtype encodings with LMUL < > SEWMIN/ELEN is reserved, implementations can set vill if they do not > support these configurations." This mean the implementation may > actually support this configuration. If that is the case, I think we > should not allow this to be configured through the vector ptrace > interface, which is designed to support 1.0 (and 0.7) specs. That > means, we should not allow this problematic configuration to pass > through riscv_vr_set(), reach user space, then the forced save. > > I would opt for validating all CSR configurations in the first place. > Could you also help enforce checks on other reserved bits as well?
Just to clarify, the suggestion is to drop the TIF_RISCV_V_FORCE_SAVE entirely and use only careful validation of input parameter in riscv_vr_set, rather than using both checks. Is that correct? If that is correct, then I assume we can rely on the simple rule ELEN == XLEN to validate vsew/vlmul supported combinations. Additionally, reserved vsew values (see 3.4.1 in spec) should also be rejected. Thanks, Sergey
