On Wed, Jul 07, 2021, Brijesh Singh wrote:
> The guest pages of the SEV-SNP VM maybe added as a private page in the
> RMP entry (assigned bit is set). The guest private pages must be
> transitioned to the hypervisor state before its freed.
Isn't this patch needed much earlier in the series, i.e. when the first RMPUPDATE
usage goes in?
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> ---
> arch/x86/kvm/svm/sev.c | 39 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 1f0635ac9ff9..4468995dd209 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1940,6 +1940,45 @@ find_enc_region(struct kvm *kvm, struct kvm_enc_region *range)
> static void __unregister_enc_region_locked(struct kvm *kvm,
> struct enc_region *region)
> {
> + struct rmpupdate val = {};
> + unsigned long i, pfn;
> + struct rmpentry *e;
> + int level, rc;
> +
> + /*
> + * The guest memory pages are assigned in the RMP table. Unassign it
> + * before releasing the memory.
> + */
> + if (sev_snp_guest(kvm)) {
> + for (i = 0; i < region->npages; i++) {
> + pfn = page_to_pfn(region->pages[i]);
> +
> + if (need_resched())
> + schedule();
This can simply be "cond_resched();"
> +
> + e = snp_lookup_page_in_rmptable(region->pages[i], &level);
> + if (unlikely(!e))
> + continue;
> +
> + /* If its not a guest assigned page then skip it. */
> + if (!rmpentry_assigned(e))
> + continue;
> +
> + /* Is the page part of a 2MB RMP entry? */
> + if (level == PG_LEVEL_2M) {
> + val.pagesize = RMP_PG_SIZE_2M;
> + pfn &= ~(KVM_PAGES_PER_HPAGE(PG_LEVEL_2M) - 1);
> + } else {
> + val.pagesize = RMP_PG_SIZE_4K;
This raises yet more questions (for me) as to the interaction between Page-Size
and Hyperivsor-Owned flags in the RMP. It also raises questions on the correctness
of zeroing the RMP entry if KVM_SEV_SNP_LAUNCH_START (in the previous patch).
> + }
> +
> + /* Transition the page to hypervisor owned. */
> + rc = rmpupdate(pfn_to_page(pfn), &val);
> + if (rc)
> + pr_err("Failed to release pfn 0x%lx ret=%d\n", pfn, rc);
This is not robust, e.g. KVM will unpin the memory and release it back to the
kernel with a stale RMP entry. Shouldn't this be a WARN+leak situation?
> + }
> + }
> +
> sev_unpin_memory(kvm, region->pages, region->npages);
> list_del(®ion->list);
> kfree(region);
> --
> 2.17.1
>
