From: Janosch Frank <frankja@linux.ibm.com>
To: Claudio Imbrenda <imbrenda@linux.ibm.com>, kvm@vger.kernel.org
Cc: cohuck@redhat.com, borntraeger@de.ibm.com, thuth@redhat.com,
pasic@linux.ibm.com, david@redhat.com,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
Ulrich.Weigand@de.ibm.com
Subject: Re: [PATCH v5 05/14] KVM: s390: pv: leak the topmost page table when destroy fails
Date: Tue, 12 Oct 2021 09:58:19 +0200 [thread overview]
Message-ID: <bffbbef0-97b0-d620-d1ea-0acb4b9ba74e@linux.ibm.com> (raw)
In-Reply-To: <20210920132502.36111-6-imbrenda@linux.ibm.com>
On 9/20/21 15:24, Claudio Imbrenda wrote:
> Each secure guest must have a unique address space control element and
> we must avoid that new guests use the same ASCE, to avoid errors.
> Since the ASCE mostly consists of the topmost page table address (and
> flags), we must not return that memory to the pool unless the ASCE is
> no longer in use.
>
> Only a successful Destroy Secure Configuration UVC will make the ASCE
> reusable again. If the Destroy Configuration UVC fails, the ASCE
> cannot be reused for a secure guest (either for the ASCE or for other
> memory areas). To avoid a collision, it must not be used again.
>
> This is a permanent error and the page becomes in practice unusable, so
> we set it aside and leak it. On failure we already leak other memory
> that belongs to the ultravisor (i.e. the variable and base storage for
> a guest) and not leaking the topmost page table was an oversight.
>
> This error should not happen unless the hardware is broken or KVM has
> some unknown serious bug.
>
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes tag?
> ---
> arch/s390/include/asm/gmap.h | 2 ++
> arch/s390/kvm/pv.c | 4 ++-
> arch/s390/mm/gmap.c | 55 ++++++++++++++++++++++++++++++++++++
> 3 files changed, 60 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h
> index 40264f60b0da..746e18bf8984 100644
> --- a/arch/s390/include/asm/gmap.h
> +++ b/arch/s390/include/asm/gmap.h
> @@ -148,4 +148,6 @@ void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long dirty_bitmap[4],
> unsigned long gaddr, unsigned long vmaddr);
> int gmap_mark_unmergeable(void);
> void s390_reset_acc(struct mm_struct *mm);
> +void s390_remove_old_asce(struct gmap *gmap);
> +int s390_replace_asce(struct gmap *gmap);
> #endif /* _ASM_S390_GMAP_H */
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index 00d272d134c2..76b0d64ce8fa 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -168,9 +168,11 @@ int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
> atomic_set(&kvm->mm->context.is_protected, 0);
> KVM_UV_EVENT(kvm, 3, "PROTVIRT DESTROY VM: rc %x rrc %x", *rc, *rrc);
> WARN_ONCE(cc, "protvirt destroy vm failed rc %x rrc %x", *rc, *rrc);
> - /* Inteded memory leak on "impossible" error */
> + /* Intended memory leak on "impossible" error */
Rather unrelated
> if (!cc)
> kvm_s390_pv_dealloc_vm(kvm);
> + else
> + s390_replace_asce(kvm->arch.gmap);
> return cc ? -EIO : 0;
Might make more sense now to do an early return so we don't have the
ternary if here.
> }
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 9bb2c7512cd5..5a138f6220c4 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2706,3 +2706,58 @@ void s390_reset_acc(struct mm_struct *mm)
> mmput(mm);
> }
> EXPORT_SYMBOL_GPL(s390_reset_acc);
> +
> +/*
> + * Remove the topmost level of page tables from the list of page tables of
> + * the gmap.
> + * This means that it will not be freed when the VM is torn down, and needs
> + * to be handled separately by the caller, unless an intentional leak is
> + * intended.
> + */
> +void s390_remove_old_asce(struct gmap *gmap)
> +{
> + struct page *old;
> +
> + old = virt_to_page(gmap->table);
> + spin_lock(&gmap->guest_table_lock);
> + list_del(&old->lru);
> + spin_unlock(&gmap->guest_table_lock);
> + /* in case the ASCE needs to be "removed" multiple times */
> + INIT_LIST_HEAD(&old->lru);
> +}
> +EXPORT_SYMBOL_GPL(s390_remove_old_asce);
Is this used anywhere else than below?
This can be static, no?
> +
> +/*
> + * Try to replace the current ASCE with another equivalent one.
> + * If the allocation of the new top level page table fails, the ASCE is not
> + * replaced.
> + * In any case, the old ASCE is removed from the list, therefore the caller
> + * has to make sure to save a pointer to it beforehands, unless an
> + * intentional leak is intended.
> + */
> +int s390_replace_asce(struct gmap *gmap)
> +{
> + unsigned long asce;
> + struct page *page;
> + void *table;
> +
> + s390_remove_old_asce(gmap);
> +
> + page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER);
> + if (!page)
> + return -ENOMEM;
> + table = page_to_virt(page);
> + memcpy(table, gmap->table, 1UL << (CRST_ALLOC_ORDER + PAGE_SHIFT));
> +
> + spin_lock(&gmap->guest_table_lock);
> + list_add(&page->lru, &gmap->crst_list);
> + spin_unlock(&gmap->guest_table_lock);
> +
> + asce = (gmap->asce & ~PAGE_MASK) | __pa(table);
> + WRITE_ONCE(gmap->asce, asce);
Are you sure we don't need the mm in write lock?
> + WRITE_ONCE(gmap->mm->context.gmap_asce, asce);
This is usually changed with the context lock held.
> + WRITE_ONCE(gmap->table, table);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(s390_replace_asce);
>
next prev parent reply other threads:[~2021-10-12 7:58 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 13:24 [PATCH v5 00/14] KVM: s390: pv: implement lazy destroy for reboot Claudio Imbrenda
2021-09-20 13:24 ` [PATCH v5 01/14] KVM: s390: pv: add macros for UVC CC values Claudio Imbrenda
2021-10-05 13:08 ` Janosch Frank
2021-09-20 13:24 ` [PATCH v5 02/14] KVM: s390: pv: avoid double free of sida page Claudio Imbrenda
2021-10-05 13:11 ` Janosch Frank
2021-10-05 13:38 ` Christian Borntraeger
2021-09-20 13:24 ` [PATCH v5 03/14] KVM: s390: pv: avoid stalls for kvm_s390_pv_init_vm Claudio Imbrenda
2021-10-05 13:20 ` Janosch Frank
2021-09-20 13:24 ` [PATCH v5 04/14] KVM: s390: pv: avoid stalls when making pages secure Claudio Imbrenda
2021-10-06 15:54 ` Christian Borntraeger
2021-10-06 16:14 ` Claudio Imbrenda
2021-10-12 7:43 ` Janosch Frank
2021-10-12 8:59 ` Christian Borntraeger
2021-09-20 13:24 ` [PATCH v5 05/14] KVM: s390: pv: leak the topmost page table when destroy fails Claudio Imbrenda
2021-10-12 7:58 ` Janosch Frank [this message]
2021-10-12 8:33 ` Claudio Imbrenda
2021-09-20 13:24 ` [PATCH v5 06/14] KVM: s390: pv: properly handle page flags for protected guests Claudio Imbrenda
2021-10-12 7:59 ` Janosch Frank
2021-10-26 11:53 ` Christian Borntraeger
2021-09-20 13:24 ` [PATCH v5 07/14] KVM: s390: pv: handle secure storage violations " Claudio Imbrenda
2021-09-20 13:24 ` [PATCH v5 08/14] KVM: s390: pv: handle secure storage exceptions for normal guests Claudio Imbrenda
2021-10-12 8:16 ` Janosch Frank
2021-10-12 8:35 ` Claudio Imbrenda
2021-10-12 12:31 ` Janosch Frank
2021-09-20 13:24 ` [PATCH v5 09/14] KVM: s390: pv: refactor s390_reset_acc Claudio Imbrenda
2021-09-20 13:24 ` [PATCH v5 10/14] KVM: s390: pv: usage counter instead of flag Claudio Imbrenda
2021-09-20 13:24 ` [PATCH v5 11/14] KVM: s390: pv: add export before import Claudio Imbrenda
2021-09-20 13:25 ` [PATCH v5 12/14] KVM: s390: pv: module parameter to fence lazy destroy Claudio Imbrenda
2021-09-20 13:25 ` [PATCH v5 13/14] KVM: s390: pv: lazy destroy for reboot Claudio Imbrenda
2021-09-20 13:25 ` [PATCH v5 14/14] KVM: s390: pv: avoid export before import if possible Claudio Imbrenda
2021-10-05 13:26 ` [PATCH v5 00/14] KVM: s390: pv: implement lazy destroy for reboot Janosch Frank
2021-10-05 14:15 ` Christian Borntraeger
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