Re: [PATCH] target/arm: Add raw_writes ops for register whose write induce TLB maintenance

[Peter Maydell]

On Fri, 3 Feb 2023 at 17:17, Eric Auger <eric.auger@redhat.com> wrote:
>
> Many registers whose 'cooked' writefns induce TLB maintenance do
> not have raw_writefn ops defined. If only the writefn ops is set
> (ie. no raw_writefn is provided), it is assumed the cooked also
> work as the raw one. For those registers it is not obvious the
> tlb_flush works on KVM mode so better/safer setting the raw write.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Suggested-by: Peter Maydell <peter.maydell@linaro.org>
>
> ---
>
> I'am not familiar with those callbacks. I have tested in kvm accelerated
> mode including migration but I fail to test with TCG. It SIGSEVs for
> me even without my additions. I am not sure whether the .raw_writefn
> must be set only for registers only doing some TLB maintenance or
> shall be set safely on other registers doing TLB maintenance + other
> state settings.
> ---
> @@ -718,16 +718,20 @@ static const ARMCPRegInfo not_v7_cp_reginfo[] = {
>       * the unified TLB ops but also the dside/iside/inner-shareable variants.
>       */
>      { .name = "TLBIALL", .cp = 15, .crn = 8, .crm = CP_ANY,
> -      .opc1 = CP_ANY, .opc2 = 0, .access = PL1_W, .writefn = tlbiall_write,
> +      .opc1 = CP_ANY, .opc2 = 0, .access = PL1_W,
> +      .writefn = tlbiall_write, .raw_writefn = raw_write,
>        .type = ARM_CP_NO_RAW },

Anything with type ARM_CP_NO_RAW shouldn't need a .raw_writefn, because
that type indication says that it's a bug if we ever call
read_raw_cp_reg() or write_raw_cp_reg() on it. (Specifically,
for KVM, we should never end up trying to do a raw read/write
for a state sync because write_list_to_cpustate() and
write_cpustate_to_list() skip NO_RAW cpregs.)

thanks
-- PMM