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Re: [PATCH v4 02/12] xen/arm: add SVE vector length field to the domain
- To: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 29 Mar 2023 12:32:23 +0200
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- Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 29 Mar 2023 10:32:36 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29.03.2023 12:01, Luca Fancellu wrote:
>> On 28 Mar 2023, at 10:36, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> Yet another question is whether both range checks (against
>> SVE_VL_MAX_BITS and zcr_max_bits) are actually necessary / useful.
>> Iirc 2048 is a hard upper bound, so zcr_max_bits being higher than
>> that value should likely lead to not using SVE at all (if it doesn't
>> already; didn't check).
>
> I think the check sve_vl_bits > zcr_max_bits is needed because from
> sve_vl_bits = sve_decode_vl(config->arch.sve_vl); I can get values above the
> maximum supported bits (zcr_max_bits), later on I will use the struct
> arch_domain
> field sve_vl to compute the size of the registers to be saved/restore
>
> Is there something I’ve missed from your comment?
Hmm, I realize my earlier response may have been ambiguous: I didn't
mean to question the presence of both checks individually. I merely
meant to question whether in addition to the zcr_max_bits check you
really also need the SVE_VL_MAX_BITS one.
Jan
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