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KVM: s390: pv: avoid export before import if possible

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If the appropriate UV feature bit is set, there is no need to perform
an export before import.

The misc feature indicates, among other things, that importing a shared
page from a different protected VM will automatically also transfer its
ownership.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Link: https://lore.kernel.org/r/20221111170632.77622-5-imbrenda@linux.ibm.com
Message-Id: <20221111170632.77622-5-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
This commit is contained in:
Claudio Imbrenda 2022-11-11 18:06:30 +01:00 committed by Janosch Frank
parent 8c516b25d6
commit afe20eb8df
1 changed files with 7 additions and 0 deletions
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7
arch/s390/kernel/uv.c
View file

@ -255,6 +255,13 @@ 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)
{
/*
* The misc feature indicates, among other things, that importing a
* shared page from a different protected VM will automatically also
* transfer its ownership.
*/
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;