[PATCHv2] kvmppc: Implement H_LOGICAL_CI_{LOAD,STORE} in KVM

David Gibson
2015-02-03T05:44:24Z

On POWER, storage caching is usually configured via the MMU - attributes
such as cache-inhibited are stored in the TLB and the hashed page table.

This makes correctly performing cache inhibited IO accesses awkward when
the MMU is turned off (real mode). Some CPU models provide special
registers to control the cache attributes of real mode load and stores but
this is not at all consistent. This is a problem in particular for SLOF,
the firmware used on KVM guests, which runs entirely in real mode, but
which needs to do IO to load the kernel.

To simplify this qemu implements two special hypercalls, H_LOGICAL_CI_LOAD
and H_LOGICAL_CI_STORE which simulate a cache-inhibited load or store to
a logical address (aka guest physical address). SLOF uses these for IO.

However, because these are implemented within qemu, not the host kernel,
these bypass any IO devices emulated within KVM itself. The simplest way
to see this problem is to attempt to boot a KVM guest from a virtio-blk
device with iothread / dataplane enabled. The iothread code relies on an
in kernel implementation of the virtio queue notification, which is not
triggered by the IO hcalls, and so the guest will stall in SLOF unable to
load the guest OS.

This patch addresses this by providing in-kernel implementations of the
2 hypercalls, which correctly scan the KVM IO bus. Any access to an
address not handled by the KVM IO bus will cause a VM exit, hitting the
qemu implementation as before.

Note that a userspace change is also required, in order to enable these
new hcall implementations with KVM_CAP_PPC_ENABLE_HCALL.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
arch/powerpc/include/asm/kvm_book3s.h | 3 ++
arch/powerpc/kvm/book3s.c | 76 +++++++++++++++++++++++++++++++++++
arch/powerpc/kvm/book3s_hv.c | 12 ++++++
arch/powerpc/kvm/book3s_pr_papr.c | 28 +++++++++++++
4 files changed, 119 insertions(+)

v2:
- Removed some debugging printk()s that were accidentally left in
- Fix endianness; like all PAPR hypercalls, these should always act
big-endian, even if the guest is little-endian (in practice this
makes no difference, since the only user is SLOF, which is always
big-endian)

diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index 942c7b1..578e550 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -292,6 +292,9 @@ static inline bool kvmppc_supports_magic_page(struct kvm_vcpu *vcpu)
return !is_kvmppc_hv_enabled(vcpu->kvm);
}

+extern int kvmppc_h_logical_ci_load(struct kvm_vcpu *vcpu);
+extern int kvmppc_h_logical_ci_store(struct kvm_vcpu *vcpu);
+
/* Magic register values loaded into r3 and r4 before the 'sc' assembly
* instruction for the OSI hypercalls */
#define OSI_SC_MAGIC_R3 0x113724FA
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index 888bf46..7b51492 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -820,6 +820,82 @@ void kvmppc_core_destroy_vm(struct kvm *kvm)
#endif
}

+int kvmppc_h_logical_ci_load(struct kvm_vcpu *vcpu)
+{
+ unsigned long size = kvmppc_get_gpr(vcpu, 4);
+ unsigned long addr = kvmppc_get_gpr(vcpu, 5);
+ u64 buf;
+ int ret;
+
+ if (!is_power_of_2(size) || (size > sizeof(buf)))
+ return H_TOO_HARD;
+
+ ret = kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, addr, size, &buf);
+ if (ret != 0)
+ return H_TOO_HARD;
+
+ switch (size) {
+ case 1:
+ kvmppc_set_gpr(vcpu, 4, *(u8 *)&buf);
+ break;
+
+ case 2:
+ kvmppc_set_gpr(vcpu, 4, be16_to_cpu(*(u16 *)&buf));
+ break;
+
+ case 4:
+ kvmppc_set_gpr(vcpu, 4, be32_to_cpu(*(u32 *)&buf));
+ break;
+
+ case 8:
+ kvmppc_set_gpr(vcpu, 4, be64_to_cpu(*(u64 *)&buf));
+ break;
+
+ default:
+ BUG();
+ }
+
+ return H_SUCCESS;
+}
+EXPORT_SYMBOL_GPL(kvmppc_h_logical_ci_load); /* For use by the kvm-pr module */
+
+int kvmppc_h_logical_ci_store(struct kvm_vcpu *vcpu)
+{
+ unsigned long size = kvmppc_get_gpr(vcpu, 4);
+ unsigned long addr = kvmppc_get_gpr(vcpu, 5);
+ unsigned long val = kvmppc_get_gpr(vcpu, 6);
+ u64 buf;
+ int ret;
+
+ switch (size) {
+ case 1:
+ *(u8 *)&buf = val;
+ break;
+
+ case 2:
+ *(u16 *)&buf = cpu_to_be16(val);
+ break;
+
+ case 4:
+ *(u32 *)&buf = cpu_to_be32(val);
+ break;
+
+ case 8:
+ *(u64 *)&buf = cpu_to_be64(val);
+ break;
+
+ default:
+ return H_TOO_HARD;
+ }
+
+ ret = kvm_io_bus_write(vcpu->kvm, KVM_MMIO_BUS, addr, size, &buf);
+ if (ret != 0)
+ return H_TOO_HARD;
+
+ return H_SUCCESS;
+}
+EXPORT_SYMBOL_GPL(kvmppc_h_logical_ci_store); /* For use by the kvm-pr module */
+
int kvmppc_core_check_processor_compat(void)
{
/*
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index de4018a..f631b76 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -706,6 +706,16 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)

/* Send the error out to userspace via KVM_RUN */
return rc;
+ case H_LOGICAL_CI_LOAD:
+ ret = kvmppc_h_logical_ci_load(vcpu);
+ if (ret == H_TOO_HARD)
+ return RESUME_HOST;
+ break;
+ case H_LOGICAL_CI_STORE:
+ ret = kvmppc_h_logical_ci_store(vcpu);
+ if (ret == H_TOO_HARD)
+ return RESUME_HOST;
+ break;
case H_SET_MODE:
ret = kvmppc_h_set_mode(vcpu, kvmppc_get_gpr(vcpu, 4),
kvmppc_get_gpr(vcpu, 5),
@@ -740,6 +750,8 @@ static int kvmppc_hcall_impl_hv(unsigned long cmd)
case H_CONFER:
case H_REGISTER_VPA:
case H_SET_MODE:
+ case H_LOGICAL_CI_LOAD:
+ case H_LOGICAL_CI_STORE:
#ifdef CONFIG_KVM_XICS
case H_XIRR:
case H_CPPR:
diff --git a/arch/powerpc/kvm/book3s_pr_papr.c b/arch/powerpc/kvm/book3s_pr_papr.c
index ce3c893..f2c75a1 100644
--- a/arch/powerpc/kvm/book3s_pr_papr.c
+++ b/arch/powerpc/kvm/book3s_pr_papr.c
@@ -258,6 +258,28 @@ static int kvmppc_h_pr_put_tce(struct kvm_vcpu *vcpu)
return EMULATE_DONE;
}

+static int kvmppc_h_pr_logical_ci_load(struct kvm_vcpu *vcpu)
+{
+ long rc;
+
+ rc = kvmppc_h_logical_ci_load(vcpu);
+ if (rc == H_TOO_HARD)
+ return EMULATE_FAIL;
+ kvmppc_set_gpr(vcpu, 3, rc);
+ return EMULATE_DONE;
+}
+
+static int kvmppc_h_pr_logical_ci_store(struct kvm_vcpu *vcpu)
+{
+ long rc;
+
+ rc = kvmppc_h_logical_ci_store(vcpu);
+ if (rc == H_TOO_HARD)
+ return EMULATE_FAIL;
+ kvmppc_set_gpr(vcpu, 3, rc);
+ return EMULATE_DONE;
+}
+
static int kvmppc_h_pr_xics_hcall(struct kvm_vcpu *vcpu, u32 cmd)
{
long rc = kvmppc_xics_hcall(vcpu, cmd);
@@ -290,6 +312,10 @@ int kvmppc_h_pr(struct kvm_vcpu *vcpu, unsigned long cmd)
clear_bit(KVM_REQ_UNHALT, &vcpu->requests);
vcpu->stat.halt_wakeup++;
return EMULATE_DONE;
+ case H_LOGICAL_CI_LOAD:
+ return kvmppc_h_pr_logical_ci_load(vcpu);
+ case H_LOGICAL_CI_STORE:
+ return kvmppc_h_pr_logical_ci_store(vcpu);
case H_XIRR:
case H_CPPR:
case H_EOI:
@@ -323,6 +349,8 @@ int kvmppc_hcall_impl_pr(unsigned long cmd)
case H_BULK_REMOVE:
case H_PUT_TCE:
case H_CEDE:
+ case H_LOGICAL_CI_LOAD:
+ case H_LOGICAL_CI_STORE:
#ifdef CONFIG_KVM_XICS
case H_XIRR:
case H_CPPR:
--
2.1.0