Re: [kvm-unit-tests PATCH 3/5] s390x: Add library functions for exiting from snippet

Nina Schoetterl-Glausch
2023-12-14T20:03:08Z

On Wed, 2023-12-13 at 17:42 +0100, Claudio Imbrenda wrote:
> On Wed, 13 Dec 2023 13:49:40 +0100
> Nina Schoetterl-Glausch <nsg@linux.ibm.com> wrote:
>
> > It is useful to be able to force an exit to the host from the snippet,
> > as well as do so while returning a value.
> > Add this functionality, also add helper functions for the host to check
> > for an exit and get or check the value.
> > Use diag 0x44 and 0x9c for this.
> > Add a guest specific snippet header file and rename the host's.
>
> you should also mention here that you are splitting snippet.h into a
> host-only part and a guest-only part

Well, I'm not splitting anything. Is it not clear that "the host's"
refers to snippet.h?

How about:
Add a guest specific snippet header file and rename snippet.h to reflect
that it is host specific.
>
> >
> > Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> > ---
> > s390x/Makefile | 1 +
> > lib/s390x/asm/arch_def.h | 13 ++++++++
> > lib/s390x/sie.h | 1 +
> > lib/s390x/snippet-guest.h | 26 ++++++++++++++++
> > lib/s390x/{snippet.h => snippet-host.h} | 9 ++++--
> > lib/s390x/sie.c | 28 +++++++++++++++++
> > lib/s390x/snippet-host.c | 40 +++++++++++++++++++++++++
> > lib/s390x/uv.c | 2 +-
> > s390x/mvpg-sie.c | 2 +-
> > s390x/pv-diags.c | 2 +-
> > s390x/pv-icptcode.c | 2 +-
> > s390x/pv-ipl.c | 2 +-
> > s390x/sie-dat.c | 2 +-
> > s390x/spec_ex-sie.c | 2 +-
> > s390x/uv-host.c | 2 +-
> > 15 files changed, 123 insertions(+), 11 deletions(-)
> > create mode 100644 lib/s390x/snippet-guest.h
> > rename lib/s390x/{snippet.h => snippet-host.h} (93%)
> > create mode 100644 lib/s390x/snippet-host.c
>
> [...]
>
> > diff --git a/lib/s390x/sie.c b/lib/s390x/sie.c
> > index 40936bd2..908b0130 100644
> > --- a/lib/s390x/sie.c
> > +++ b/lib/s390x/sie.c
> > @@ -42,6 +42,34 @@ void sie_check_validity(struct vm *vm, uint16_t vir_exp)
> > report(vir_exp == vir, "VALIDITY: %x", vir);
> > }
> >
> > +bool sie_is_diag_icpt(struct vm *vm, unsigned int diag)
> > +{
> > + uint32_t ipb = vm->sblk->ipb;
> > + uint64_t code;
>
> uint64_t code = 0;
>
> > + uint16_t displace;
> > + uint8_t base;
> > + bool ret = true;
>
> bool ret;
>
> > +
> > + ret = ret && vm->sblk->icptcode == ICPT_INST;
> > + ret = ret && (vm->sblk->ipa & 0xff00) == 0x8300;
>
> ret = vm->sblk->icptcode == ICPT_INST && (vm->sblk->ipa & 0xff00) ==
> 0x8300;

(*) see below
>
> > + switch (diag) {
> > + case 0x44:
> > + case 0x9c:
> > + ret = ret && !(ipb & 0xffff);
> > + ipb >>= 16;
> > + displace = ipb & 0xfff;
>
> maybe it's more readable to avoid shifting thigs around all the time:

I don't know, now I gotta be able to do rudimentary arithmetic :D
I don't really have a preference.
I wonder if defining a bit field would be worth it.
>
> displace = (ipb >> 16) & 0xfff;
> base = (ipb >> 28) & 0xf;
> if (base)
> code = vm->....[base];
> code = (code + displace) & 0xffff;
> if (ipb & 0xffff || code != diag)
> return false;
>
> > + ipb >>= 12;
> > + base = ipb & 0xf;
> > + code = base ? vm->save_area.guest.grs[base] + displace : displace;
> > + code &= 0xffff;
> > + ret = ret && (code == diag);
> > + break;
> > + default:
> > + abort(); /* not implemented */
> > + }
> > + return ret;
>
> although I have the feeling that this would be more readable if you
> would check diag immediately, and avoid using ret

Not sure what you mean, do you want an early return at (*)?
>
> > +}
> > +
> > void sie_handle_validity(struct vm *vm)
> > {
> > if (vm->sblk->icptcode != ICPT_VALIDITY)
> > diff --git a/lib/s390x/snippet-host.c b/lib/s390x/snippet-host.c
> > new file mode 100644
> > index 00000000..a829c1d5
> > --- /dev/null
> > +++ b/lib/s390x/snippet-host.c
> > @@ -0,0 +1,40 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Snippet functionality for the host.
> > + *
> > + * Copyright IBM Corp. 2023
> > + */
> > +
> > +#include <libcflat.h>
> > +#include <snippet-host.h>
> > +#include <sie.h>
> > +
> > +bool snippet_check_force_exit(struct vm *vm)
> > +{
> > + bool r;
> > +
> > + r = sie_is_diag_icpt(vm, 0x44);
> > + report(r, "guest forced exit");
> > + return r;
> > +}
> > +
> > +bool snippet_get_force_exit_value(struct vm *vm, uint64_t *value)
> > +{
> > + struct kvm_s390_sie_block *sblk = vm->sblk;
> > +
> > + if (sie_is_diag_icpt(vm, 0x9c)) {
> > + *value = vm->save_area.guest.grs[(sblk->ipa & 0xf0) >> 4];
> > + report_pass("guest forced exit with value: 0x%lx", *value);
> > + return true;
> > + }
> > + report_fail("guest forced exit with value");
> > + return false;
> > +}
> > +
> > +void snippet_check_force_exit_value(struct vm *vm, uint64_t value_exp)
> > +{
> > + uint64_t value;
> > +
> > + if (snippet_get_force_exit_value(vm, &value))
> > + report(value == value_exp, "guest exit value matches 0x%lx", value_exp);
> > +}
>
> from a readability and a consistency perspective, it would be better if
> the functions would only check stuff and return a bool or a value, and
> do the report() in the body of the testcase

Hmm, I chose to do the report in order to be consistent with check_pgm_int_code.
>
>
> …