[PATCH kernel v2] KVM: PPC: Allocate guest TCEs on demand too
Alexey Kardashevskiy
aik at ozlabs.ru
Fri Mar 1 12:38:27 AEDT 2019
We already allocate hardware TCE tables in multiple levels and skip
intermediate levels when we can, now it is a turn of the KVM TCE tables.
Thankfully these are allocated already in 2 levels.
This moves the table's last level allocation from the creating helper to
kvmppc_tce_put() and kvm_spapr_tce_fault().
This adds kvmppc_rm_ioba_validate() to do an additional test if
the consequent kvmppc_tce_put() needs a page which has not been allocated;
if this is the case, we bail out to virtual mode handlers.
Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
---
Changes:
v2:
* added kvm mutex around alloc_page to prevent races; in both place we
test the pointer, if NULL, then take a lock and check again so on a fast
path we do not take a lock at all
---
For NVLink2 passthrough guests with 128TiB DMA windows and very fragmented
system RAM the difference is gigabytes of RAM.
---
arch/powerpc/kvm/book3s_64_vio.c | 29 ++++++------
arch/powerpc/kvm/book3s_64_vio_hv.c | 69 ++++++++++++++++++++++++++---
2 files changed, 79 insertions(+), 19 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index f02b049..7eed8c9 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -228,7 +228,8 @@ static void release_spapr_tce_table(struct rcu_head *head)
unsigned long i, npages = kvmppc_tce_pages(stt->size);
for (i = 0; i < npages; i++)
- __free_page(stt->pages[i]);
+ if (stt->pages[i])
+ __free_page(stt->pages[i]);
kfree(stt);
}
@@ -242,6 +243,20 @@ static vm_fault_t kvm_spapr_tce_fault(struct vm_fault *vmf)
return VM_FAULT_SIGBUS;
page = stt->pages[vmf->pgoff];
+ if (!page) {
+ mutex_lock(&stt->kvm->lock);
+ page = stt->pages[vmf->pgoff];
+ if (!page) {
+ page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ if (!page) {
+ mutex_unlock(&stt->kvm->lock);
+ return VM_FAULT_OOM;
+ }
+ stt->pages[vmf->pgoff] = page;
+ }
+ mutex_unlock(&stt->kvm->lock);
+ }
+
get_page(page);
vmf->page = page;
return 0;
@@ -296,7 +311,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
struct kvmppc_spapr_tce_table *siter;
unsigned long npages, size = args->size;
int ret = -ENOMEM;
- int i;
if (!args->size || args->page_shift < 12 || args->page_shift > 34 ||
(args->offset + args->size > (ULLONG_MAX >> args->page_shift)))
@@ -320,12 +334,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
stt->kvm = kvm;
INIT_LIST_HEAD_RCU(&stt->iommu_tables);
- for (i = 0; i < npages; i++) {
- stt->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
- if (!stt->pages[i])
- goto fail;
- }
-
mutex_lock(&kvm->lock);
/* Check this LIOBN hasn't been previously allocated */
@@ -352,11 +360,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
if (ret >= 0)
return ret;
- fail:
- for (i = 0; i < npages; i++)
- if (stt->pages[i])
- __free_page(stt->pages[i]);
-
kfree(stt);
fail_acct:
kvmppc_account_memlimit(kvmppc_stt_pages(npages), false);
diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
index 2206bc7..a0912d5 100644
--- a/arch/powerpc/kvm/book3s_64_vio_hv.c
+++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
@@ -158,23 +158,76 @@ static u64 *kvmppc_page_address(struct page *page)
return (u64 *) page_address(page);
}
+/*
+ * TCEs pages are allocated in kvmppc_tce_put() which won't be able to do so
+ * in real mode.
+ * Check if kvmppc_tce_put() can succeed in real mode, i.e. a TCEs page is
+ * allocated or not required (when clearing a tce entry).
+ */
+static long kvmppc_rm_ioba_validate(struct kvmppc_spapr_tce_table *stt,
+ unsigned long ioba, unsigned long npages, bool clearing)
+{
+ unsigned long i, sttpage, sttpages;
+ unsigned long ret = kvmppc_ioba_validate(stt, ioba, npages);
+
+ if (ret)
+ return ret;
+ /*
+ * clearing==true says kvmppc_tce_put won't be allocating pages
+ * for empty tces.
+ */
+ if (clearing)
+ return H_SUCCESS;
+
+ sttpage = ((ioba >> stt->page_shift) - stt->offset) / TCES_PER_PAGE;
+ sttpages = (npages + TCES_PER_PAGE - 1) / TCES_PER_PAGE;
+ for (i = sttpage; i < sttpage + sttpages; ++i)
+ if (!stt->pages[i])
+ return H_TOO_HARD;
+
+ return H_SUCCESS;
+}
+
/*
* Handles TCE requests for emulated devices.
* Puts guest TCE values to the table and expects user space to convert them.
* Called in both real and virtual modes.
* Cannot fail so kvmppc_tce_validate must be called before it.
*
- * WARNING: This will be called in real-mode on HV KVM and virtual
- * mode on PR KVM
+ * WARNING: This will be called in real-mode on HV HPT KVM and virtual
+ * mode on PR KVM or HV radix KVM
*/
void kvmppc_tce_put(struct kvmppc_spapr_tce_table *stt,
unsigned long idx, unsigned long tce)
{
struct page *page;
u64 *tbl;
+ unsigned long sttpage;
idx -= stt->offset;
- page = stt->pages[idx / TCES_PER_PAGE];
+ sttpage = idx / TCES_PER_PAGE;
+ page = stt->pages[sttpage];
+
+ if (!page) {
+ /* We allow any TCE, not just with read|write permissions */
+ if (!tce)
+ return;
+ /*
+ * We must not end up here in real mode,
+ * kvmppc_rm_ioba_validate() takes care of this.
+ */
+ mutex_lock(&stt->kvm->lock);
+ page = stt->pages[sttpage];
+ if (!page) {
+ page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ if (WARN_ON_ONCE(!page)) {
+ mutex_unlock(&stt->kvm->lock);
+ return;
+ }
+ stt->pages[sttpage] = page;
+ }
+ mutex_unlock(&stt->kvm->lock);
+ }
tbl = kvmppc_page_address(page);
tbl[idx % TCES_PER_PAGE] = tce;
@@ -381,7 +434,7 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
if (!stt)
return H_TOO_HARD;
- ret = kvmppc_ioba_validate(stt, ioba, 1);
+ ret = kvmppc_rm_ioba_validate(stt, ioba, 1, tce == 0);
if (ret != H_SUCCESS)
return ret;
@@ -480,7 +533,7 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
if (tce_list & (SZ_4K - 1))
return H_PARAMETER;
- ret = kvmppc_ioba_validate(stt, ioba, npages);
+ ret = kvmppc_rm_ioba_validate(stt, ioba, npages, false);
if (ret != H_SUCCESS)
return ret;
@@ -583,7 +636,7 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
if (!stt)
return H_TOO_HARD;
- ret = kvmppc_ioba_validate(stt, ioba, npages);
+ ret = kvmppc_rm_ioba_validate(stt, ioba, npages, tce_value == 0);
if (ret != H_SUCCESS)
return ret;
@@ -635,6 +688,10 @@ long kvmppc_h_get_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
idx = (ioba >> stt->page_shift) - stt->offset;
page = stt->pages[idx / TCES_PER_PAGE];
+ if (!page) {
+ vcpu->arch.regs.gpr[4] = 0;
+ return H_SUCCESS;
+ }
tbl = (u64 *)page_address(page);
vcpu->arch.regs.gpr[4] = tbl[idx % TCES_PER_PAGE];
--
2.17.1
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