@@ -1569,7 +1569,7 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr, int shift,
spapr_set_all_lpcrs(0, LPCR_HR | LPCR_UPRT);
}
-void spapr_setup_hpt_and_vrma(SpaprMachineState *spapr)
+void spapr_setup_hpt(SpaprMachineState *spapr)
{
int hpt_shift;
@@ -1585,10 +1585,16 @@ void spapr_setup_hpt_and_vrma(SpaprMachineState *spapr)
}
spapr_reallocate_hpt(spapr, hpt_shift, &error_fatal);
- if (spapr->vrma_adjust) {
+ if (kvm_enabled()) {
hwaddr vrma_limit = kvmppc_vrma_limit(spapr->htab_shift);
- spapr->rma_size = MIN(spapr_node0_size(MACHINE(spapr)), vrma_limit);
+ /* Check our RMA fits in the possible VRMA */
+ if (vrma_limit < spapr->rma_size) {
+ error_report("Unable to create %" HWADDR_PRIu
+ "MiB RMA (VRMA only allows %" HWADDR_PRIu "MiB",
+ spapr->rma_size / MiB, vrma_limit / MiB);
+ exit(EXIT_FAILURE);
+ }
}
}
@@ -1628,7 +1634,7 @@ static void spapr_machine_reset(MachineState *machine)
spapr->patb_entry = PATE1_GR;
spapr_set_all_lpcrs(LPCR_HR | LPCR_UPRT, LPCR_HR | LPCR_UPRT);
} else {
- spapr_setup_hpt_and_vrma(spapr);
+ spapr_setup_hpt(spapr);
}
qemu_devices_reset();
@@ -2696,20 +2702,6 @@ static void spapr_machine_init(MachineState *machine)
spapr->rma_size = node0_size;
- /* With KVM, we don't actually know whether KVM supports an
- * unbounded RMA (PR KVM) or is limited by the hash table size
- * (HV KVM using VRMA), so we always assume the latter
- *
- * In that case, we also limit the initial allocations for RTAS
- * etc... to 256M since we have no way to know what the VRMA size
- * is going to be as it depends on the size of the hash table
- * which isn't determined yet.
- */
- if (kvm_enabled()) {
- spapr->vrma_adjust = 1;
- spapr->rma_size = MIN(spapr->rma_size, 0x10000000);
- }
-
/* Actually we don't support unbounded RMA anymore since we added
* proper emulation of HV mode. The max we can get is 16G which
* also happens to be what we configure for PAPR mode so make sure
@@ -1458,7 +1458,7 @@ static void spapr_check_setup_free_hpt(SpaprMachineState *spapr,
spapr_free_hpt(spapr);
} else if (!(patbe_new & PATE1_GR)) {
/* RADIX->HASH || NOTHING->HASH : Allocate HPT */
- spapr_setup_hpt_and_vrma(spapr);
+ spapr_setup_hpt(spapr);
}
return;
}
@@ -1846,7 +1846,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
* (because the guest isn't going to use radix) then set it up here. */
if ((spapr->patb_entry & PATE1_GR) && !guest_radix) {
/* legacy hash or new hash: */
- spapr_setup_hpt_and_vrma(spapr);
+ spapr_setup_hpt(spapr);
}
if (fdt_bufsize < sizeof(hdr)) {
@@ -156,7 +156,6 @@ struct SpaprMachineState {
SpaprPendingHpt *pending_hpt; /* in-progress resize */
hwaddr rma_size;
- int vrma_adjust;
uint32_t fdt_size;
uint32_t fdt_initial_size;
void *fdt_blob;
@@ -795,7 +794,7 @@ void *spapr_build_fdt(SpaprMachineState *spapr, bool reset, size_t space);
void spapr_events_init(SpaprMachineState *sm);
void spapr_dt_events(SpaprMachineState *sm, void *fdt);
void close_htab_fd(SpaprMachineState *spapr);
-void spapr_setup_hpt_and_vrma(SpaprMachineState *spapr);
+void spapr_setup_hpt(SpaprMachineState *spapr);
void spapr_free_hpt(SpaprMachineState *spapr);
SpaprTceTable *spapr_tce_new_table(DeviceState *owner, uint32_t liobn);
void spapr_tce_table_enable(SpaprTceTable *tcet,
The Real Mode Area (RMA) is the part of memory which a guest can access when in real (MMU off) mode. Of course, for a guest under KVM, the MMU isn't really turned off, it's just in a special translation mode - Virtual Real Mode Area (VRMA) - which looks like real mode in guest mode. The mechanics of how this works when using the hash MMU (HPT) put a constraint on the size of the RMA, which depends on the size of the HPT. So, the latter part of spapr_setup_hpt_and_vrma() clamps the RMA we advertise to the guest based on this VRMA limit. There are several things wrong with this: 1) spapr_setup_hpt_and_vrma() doesn't actually clamp, it takes the minimum of Node 0 memory size and the VRMA limit. That will *often* work the same as clamping, but there can be other constraints on RMA size which supersede Node 0 memory size. We have real bugs caused by this (currently worked around in the guest kernel) 2) Some callers of spapr_setup_hpt_and_vrma() are in a situation where we're past the point that we can actually advertise an RMA limit to the guest 3) But most fundamentally, the VRMA limit depends on host configuration (page size) which shouldn't be visible to the guest, but this partially exposes it. This can cause problems with migration in certain edge cases, although we will mostly get away with it. In practice, this clamping is almost never applied anyway. With 64kiB pages and the normal rules for sizing of the HPT, the theoretical VRMA limit will be 4x(guest memory size) and so never hit. It will hit with 4kiB pages, where it will be (guest memory size)/4. However all mainstream distro kernels for POWER have used a 64kiB page size for at least 10 years. So, simply replace this logic with a check that the RMA we've calculated based only on guest visible configuration will fit within the host implied VRMA limit. This can break if running HPT guests on a host kernel with 4kiB page size. As noted that's very rare. There also exist several possible workarounds: * Change the host kernel to use 64kiB pages * Use radix MMU (RPT) guests instead of HPT * Use 64kiB hugepages on the host to back guest memory * Increase the guest memory size so that the RMA hits one of the fixed limits before the RMA limit. This is relatively easy on POWER8 which has a 16GiB limit, harder on POWER9 which has a 1TiB limit. * Use a guest NUMA configuration which artificially constrains the RMA within the VRMA limit (the RMA must always fit within Node 0). Previously, on KVM, we also temporarily reduced the rma_size to 256M so that the we'd load the kernel and initrd safely, regardless of the VRMA limit. This was a) confusing, b) could significantly limit the size of images we could load and c) introduced a behavioural difference between KVM and TCG. So we remove that as well. Signed-off-by: David Gibson <david@gibson.dropbear.id.au> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru> --- hw/ppc/spapr.c | 28 ++++++++++------------------ hw/ppc/spapr_hcall.c | 4 ++-- include/hw/ppc/spapr.h | 3 +-- 3 files changed, 13 insertions(+), 22 deletions(-)