Re: [PATCH 2/4] powerpc kvm: added multiple TCEs requests support

Alexey Kardashevskiy <aik@xxxxxxxxx> · Mon, 18 Feb 2013 19:14:29 +1100

On 15/02/13 14:24, Paul Mackerras wrote:
On Mon, Feb 11, 2013 at 11:12:41PM +1100, aik@xxxxxxxxx wrote:

+static long emulated_h_put_tce(struct kvmppc_spapr_tce_table *stt,
+		unsigned long ioba, unsigned long tce)
+{
+	unsigned long idx = ioba >> SPAPR_TCE_SHIFT;
+	struct page *page;
+	u64 *tbl;
+
+	/* udbg_printf("H_PUT_TCE: liobn 0x%lx => stt=%p  window_size=0x%x\n", */
+	/* 	    liobn, stt, stt->window_size); */
+	if (ioba >= stt->window_size) {
+		pr_err("%s failed on ioba=%lx\n", __func__, ioba);

Doesn't this give the guest a way to spam the host logs?  And in fact
printk in real mode is potentially problematic.  I would just leave
out this statement.

+		return H_PARAMETER;
+	}
+
+	page = stt->pages[idx / TCES_PER_PAGE];
+	tbl = (u64 *)page_address(page);

I would like to see an explanation of why we are confident that
page_address() will work correctly in real mode, across all the
combinations of config options that we can have for a ppc64 book3s
kernel.

It was there before this patch, I just moved it so I would think it has 
been explained before :)

There is no combination on PPC to get WANT_PAGE_VIRTUAL enabled.
CONFIG_HIGHMEM is supported for PPC32 only so HASHED_PAGE_VIRTUAL is not 
enabled on PPC64 either.

So this definition is supposed to work on PPC64:
#define page_address(page) lowmem_page_address(page)

where lowmem_page_address() is arithmetic operation on a page struct address:
static __always_inline void *lowmem_page_address(const struct page *page)
{
	return __va(PFN_PHYS(page_to_pfn(page)));
}

PPC32 will use page_address() from mm/highmem.c, I need some lesson about 
memory layout in 32bit but for now I cannot see how it can possibly fail here.



+
+	/* FIXME: Need to validate the TCE itself */
+	/* udbg_printf("tce @ %p\n", &tbl[idx % TCES_PER_PAGE]); */
+	tbl[idx % TCES_PER_PAGE] = tce;
+
+	return H_SUCCESS;
+}
+
+/*
+ * Real mode handlers
   */
  long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
  		      unsigned long ioba, unsigned long tce)
  {
-	struct kvm *kvm = vcpu->kvm;
  	struct kvmppc_spapr_tce_table *stt;

-	/* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
-	/* 	    liobn, ioba, tce); */
+	stt = find_tce_table(vcpu, liobn);
+	/* Didn't find the liobn, put it to userspace */
+	if (!stt)
+		return H_TOO_HARD;
+
+	/* Emulated IO */
+	return emulated_h_put_tce(stt, ioba, tce);
+}
+
+long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
+		unsigned long liobn, unsigned long ioba,
+		unsigned long tce_list,	unsigned long npages)
+{
+	struct kvmppc_spapr_tce_table *stt;
+	long i, ret = 0;
+	unsigned long *tces;
+
+	stt = find_tce_table(vcpu, liobn);
+	/* Didn't find the liobn, put it to userspace */
+	if (!stt)
+		return H_TOO_HARD;

-	list_for_each_entry(stt, &kvm->arch.spapr_tce_tables, list) {
-		if (stt->liobn == liobn) {
-			unsigned long idx = ioba >> SPAPR_TCE_SHIFT;
-			struct page *page;
-			u64 *tbl;
+	tces = (void *) get_real_address(vcpu, tce_list, false, NULL, NULL);
+	if (!tces)
+		return H_TOO_HARD;

-			/* udbg_printf("H_PUT_TCE: liobn 0x%lx => stt=%p  window_size=0x%x\n", */
-			/* 	    liobn, stt, stt->window_size); */
-			if (ioba >= stt->window_size)
-				return H_PARAMETER;
+	/* Emulated IO */
+	for (i = 0; (i < npages) && !ret; ++i, ioba += IOMMU_PAGE_SIZE)
+		ret = emulated_h_put_tce(stt, ioba, tces[i]);

So, tces is a pointer to somewhere inside a real page.  Did we check
somewhere that tces[npages-1] is in the same page as tces[0]?  If so,
I missed it.  If we didn't, then we probably should check and do
something about it.


-			page = stt->pages[idx / TCES_PER_PAGE];
-			tbl = (u64 *)page_address(page);
+	return ret;
+}

-			/* FIXME: Need to validate the TCE itself */
-			/* udbg_printf("tce @ %p\n", &tbl[idx % TCES_PER_PAGE]); */
-			tbl[idx % TCES_PER_PAGE] = tce;
-			return H_SUCCESS;
-		}
-	}
+long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
+		unsigned long liobn, unsigned long ioba,
+		unsigned long tce_value, unsigned long npages)
+{
+	struct kvmppc_spapr_tce_table *stt;
+	long i, ret = 0;
+
+	stt = find_tce_table(vcpu, liobn);
+	/* Didn't find the liobn, put it to userspace */
+	if (!stt)
+		return H_TOO_HARD;

-	/* Didn't find the liobn, punt it to userspace */
-	return H_TOO_HARD;
+	/* Emulated IO */
+	for (i = 0; (i < npages) && !ret; ++i, ioba += IOMMU_PAGE_SIZE)
+		ret = emulated_h_put_tce(stt, ioba, tce_value);
+
+	return ret;
+}
+
+/*
+ * Virtual mode handlers
+ */
+extern long kvmppc_virtmode_h_put_tce(struct kvm_vcpu *vcpu,
+		unsigned long liobn, unsigned long ioba,
+		unsigned long tce)
+{
+	/* At the moment emulated IO is handled the same way */
+	return kvmppc_h_put_tce(vcpu, liobn, ioba, tce);
+}
+
+extern long kvmppc_virtmode_h_put_tce_indirect(struct kvm_vcpu *vcpu,
+		unsigned long liobn, unsigned long ioba,
+		unsigned long tce_list, unsigned long npages)
+{
+	struct kvmppc_spapr_tce_table *stt;
+	unsigned long *tces;
+	long ret = 0, i;
+
+	stt = find_tce_table(vcpu, liobn);
+	/* Didn't find the liobn, put it to userspace */
+	if (!stt)
+		return H_TOO_HARD;
+
+	tces = (void *) get_virt_address(vcpu, tce_list, false, NULL, NULL);
+	if (!tces)
+		return H_TOO_HARD;
+
+	/* Emulated IO */
+	for (i = 0; (i < npages) && !ret; ++i, ioba += IOMMU_PAGE_SIZE)
+		ret = emulated_h_put_tce(stt, ioba, tces[i]);

Same comment here about tces[i] overflowing a page boundary.

+
+	return ret;
+}
+
+extern long kvmppc_virtmode_h_stuff_tce(struct kvm_vcpu *vcpu,
+		unsigned long liobn, unsigned long ioba,
+		unsigned long tce_value, unsigned long npages)
+{
+	/* At the moment emulated IO is handled the same way */
+	return kvmppc_h_stuff_tce(vcpu, liobn, ioba, tce_value, npages);
  }

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 71d0c90..13c8436 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -515,6 +515,29 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
  					kvmppc_get_gpr(vcpu, 5),
  					kvmppc_get_gpr(vcpu, 6));
  		break;
+	case H_PUT_TCE:
+		ret = kvmppc_virtmode_h_put_tce(vcpu, kvmppc_get_gpr(vcpu, 4),
+					        kvmppc_get_gpr(vcpu, 5),
+					        kvmppc_get_gpr(vcpu, 6));
+		if (ret == H_TOO_HARD)
+			return RESUME_HOST;
+		break;
+	case H_PUT_TCE_INDIRECT:
+		ret = kvmppc_virtmode_h_put_tce_indirect(vcpu, kvmppc_get_gpr(vcpu, 4),
+					        kvmppc_get_gpr(vcpu, 5),
+					        kvmppc_get_gpr(vcpu, 6),
+						kvmppc_get_gpr(vcpu, 7));
+		if (ret == H_TOO_HARD)
+			return RESUME_HOST;
+		break;
+	case H_STUFF_TCE:
+		ret = kvmppc_virtmode_h_stuff_tce(vcpu, kvmppc_get_gpr(vcpu, 4),
+					        kvmppc_get_gpr(vcpu, 5),
+					        kvmppc_get_gpr(vcpu, 6),
+						kvmppc_get_gpr(vcpu, 7));
+		if (ret == H_TOO_HARD)
+			return RESUME_HOST;
+		break;
  	default:
  		return RESUME_HOST;
  	}
[snip]
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 70739a0..95614c7 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -383,6 +383,9 @@ int kvm_dev_ioctl_check_extension(long ext)
  		r = 1;
  		break;
  #endif
+	case KVM_CAP_PPC_MULTITCE:
+		r = 1;
+		break;
  	default:
  		r = 0;
  		break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index e6e5d4b..26e2b271 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -635,6 +635,7 @@ struct kvm_ppc_smmu_info {
  #define KVM_CAP_IRQFD_RESAMPLE 82
  #define KVM_CAP_PPC_BOOKE_WATCHDOG 83
  #define KVM_CAP_PPC_HTAB_FD 84
+#define KVM_CAP_PPC_MULTITCE 87

The capability should be described in
Documentation/virtual/kvm/api.txt.

Is it enough description?

===
4.79 KVM_CAP_PPC_MULTITCE

Architectures: ppc
Parameters: none
Returns: 0 on success; -1 on error

This capability enables the guest to put/remove multiple TCE entries
per hypercall which significanly accelerates DMA operations for PPC KVM
guests.

When this capability is enabled, H_PUT_TCE_INDIRECT and H_STUFF_TCE are
expected to occur rather than H_PUT_TCE which supports only one TCE entry
per call.
===


--
Alexey
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