linux-kernel - Re: [PATCH v10 18/19] KVM: s390: pv: avoid export before import if possible

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Message-ID: <d76e875c360c53d6bd03c3f2767c90dcc4ca6df9.camel@linux.ibm.com>
Date:   Mon, 30 May 2022 12:07:43 +0200
From:   Nico Boehr <nrb@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     borntraeger@...ibm.com, frankja@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, scgl@...ux.ibm.com,
        mimu@...ux.ibm.com
Subject: Re: [PATCH v10 18/19] KVM: s390: pv: avoid export before import if
 possible

On Thu, 2022-04-14 at 10:03 +0200, Claudio Imbrenda wrote:

> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index e358b8bd864b..43393568f844 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -236,7 +236,8 @@ static int make_secure_pte(pte_t *ptep, unsigned
> long addr,
>  
>  static bool should_export_before_import(struct uv_cb_header *uvcb,
> struct mm_struct *mm)
>  {
> -       return uvcb->cmd != UVC_CMD_UNPIN_PAGE_SHARED &&
> +       return !test_bit_inv(BIT_UV_FEAT_MISC,
> &uv_info.uv_feature_indications) &&
> +               uvcb->cmd != UVC_CMD_UNPIN_PAGE_SHARED &&
>                 atomic_read(&mm->context.protected_count) > 1;

This might be nicer to read like this:

if (test_bit_inv(BIT_UV_FEAT_MISC, &uv_info.uv_feature_indications))
  return false;

if (uvcb->cmd == UVC_CMD_UNPIN_PAGE_SHARED)
  return false;

return atomic_read(&mm->context.protected_count) > 1;