Re: [Qemu-devel] [PATCH v1] s390x/kvm: Configure page size after memory has actually been initialized

[Igor Mammedov]

On Wed, 27 Mar 2019 14:59:44 +0100
David Hildenbrand <address@hidden> wrote:

> Right now we configure the pagesize quite early, when initializing KVM.
> This is long before system memory is actually allocated via
> memory_region_allocate_system_memory(), and therefore memory backends
> marked as mapped.
> 
> Instead, let's configure the maximum page size after initializing
> memory in s390_memory_init(). cap_hpage_1m is still properly
> configured before creating any CPUs, and therefore before configuring
> the CPU model and eventually enabling CMMA.
> 
> We might later want to replace qemu_getrampagesize() by another
> detection mechanism, e.g. only looking at mapped, initial memory.
> We don't support any memory devices yet, and if so, we can always reject
> devices with a page size bigger than the initial page size when
> hotplugging. qemu_getrampagesize() should work for now, especially when
> converting it to only look at mapped backends.
> 
> Signed-off-by: David Hildenbrand <address@hidden>

Acked-by: Igor Mammedov <address@hidden>

> ---
> 
> I only did a quick sanity test - I don't have a system with huge page
> support around to test. I did a compile for both KVM and TCG.
> 
> As Conny is on vacation and Christian is also not around, I guess it is
> okay that David G. will pick this up for now, to eventually make
> qemu_getrampagesize() only check mapped backends.
> 
>  hw/s390x/s390-virtio-ccw.c |  9 +++++++++
>  target/s390x/cpu.c         |  7 +++++++
>  target/s390x/cpu.h         |  1 +
>  target/s390x/kvm-stub.c    |  4 ++++
>  target/s390x/kvm.c         | 35 ++++++++++++++---------------------
>  target/s390x/kvm_s390x.h   |  1 +
>  6 files changed, 36 insertions(+), 21 deletions(-)
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index d11069b860..b968bccc87 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -15,6 +15,7 @@
>  #include "cpu.h"
>  #include "hw/boards.h"
>  #include "exec/address-spaces.h"
> +#include "exec/ram_addr.h"
>  #include "hw/s390x/s390-virtio-hcall.h"
>  #include "hw/s390x/sclp.h"
>  #include "hw/s390x/s390_flic.h"
> @@ -163,6 +164,7 @@ static void s390_memory_init(ram_addr_t mem_size)
>      MemoryRegion *sysmem = get_system_memory();
>      ram_addr_t chunk, offset = 0;
>      unsigned int number = 0;
> +    Error *local_err = NULL;
>      gchar *name;
>  
>      /* allocate RAM for core */
> @@ -182,6 +184,12 @@ static void s390_memory_init(ram_addr_t mem_size)
>      }
>      g_free(name);
>  
> +    /* Configure the maximum page size */
> +    s390_set_max_pagesize(qemu_getrampagesize(), &local_err);
> +    if (local_err) {
> +        error_report_err(local_err);
> +        exit(EXIT_FAILURE);
> +    }
>      /* Initialize storage key device */
>      s390_skeys_init();
>      /* Initialize storage attributes device */
> @@ -253,6 +261,7 @@ static void ccw_init(MachineState *machine)
>      DeviceState *dev;
>  
>      s390_sclp_init();
> +    /* init memory + setup max page size. Required for the CPU model */
>      s390_memory_init(machine->ram_size);
>  
>      /* init CPUs (incl. CPU model) early so s390_has_feature() works */
> diff --git a/target/s390x/cpu.c b/target/s390x/cpu.c
> index 698dd9cb82..b58ef0a8ef 100644
> --- a/target/s390x/cpu.c
> +++ b/target/s390x/cpu.c
> @@ -399,6 +399,13 @@ int s390_set_memory_limit(uint64_t new_limit, uint64_t 
> *hw_limit)
>      return 0;
>  }
>  
> +void s390_set_max_pagesize(uint64_t pagesize, Error **errp)
> +{
> +    if (kvm_enabled()) {
> +        kvm_s390_set_max_pagesize(pagesize, errp);
> +    }
> +}
> +
>  void s390_cmma_reset(void)
>  {
>      if (kvm_enabled()) {
> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> index cb6d77053a..c14be2b5ba 100644
> --- a/target/s390x/cpu.h
> +++ b/target/s390x/cpu.h
> @@ -734,6 +734,7 @@ static inline void s390_do_cpu_load_normal(CPUState *cs, 
> run_on_cpu_data arg)
>  /* cpu.c */
>  void s390_crypto_reset(void);
>  int s390_set_memory_limit(uint64_t new_limit, uint64_t *hw_limit);
> +void s390_set_max_pagesize(uint64_t pagesize, Error **errp);
>  void s390_cmma_reset(void);
>  void s390_enable_css_support(S390CPU *cpu);
>  int s390_assign_subch_ioeventfd(EventNotifier *notifier, uint32_t sch_id,
> diff --git a/target/s390x/kvm-stub.c b/target/s390x/kvm-stub.c
> index bf7795e47a..22b4514ca6 100644
> --- a/target/s390x/kvm-stub.c
> +++ b/target/s390x/kvm-stub.c
> @@ -93,6 +93,10 @@ int kvm_s390_set_mem_limit(uint64_t new_limit, uint64_t 
> *hw_limit)
>      return 0;
>  }
>  
> +void kvm_s390_set_max_pagesize(uint64_t pagesize, Error **errp)
> +{
> +}
> +
>  void kvm_s390_crypto_reset(void)
>  {
>  }
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index 19530fb94e..bee73dc1a4 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -283,44 +283,37 @@ void kvm_s390_crypto_reset(void)
>      }
>  }
>  
> -static int kvm_s390_configure_mempath_backing(KVMState *s)
> +void kvm_s390_set_max_pagesize(uint64_t pagesize, Error **errp)
>  {
> -    size_t path_psize = qemu_getrampagesize();
> -
> -    if (path_psize == 4 * KiB) {
> -        return 0;
> +    if (pagesize == 4 * KiB) {
> +        return;
>      }
>  
>      if (!hpage_1m_allowed()) {
> -        error_report("This QEMU machine does not support huge page "
> -                     "mappings");
> -        return -EINVAL;
> +        error_setg(errp, "This QEMU machine does not support huge page "
> +                   "mappings");
> +        return;
>      }
>  
> -    if (path_psize != 1 * MiB) {
> -        error_report("Memory backing with 2G pages was specified, "
> -                     "but KVM does not support this memory backing");
> -        return -EINVAL;
> +    if (pagesize != 1 * MiB) {
> +        error_setg(errp, "Memory backing with 2G pages was specified, "
> +                   "but KVM does not support this memory backing");
> +        return;
>      }
>  
> -    if (kvm_vm_enable_cap(s, KVM_CAP_S390_HPAGE_1M, 0)) {
> -        error_report("Memory backing with 1M pages was specified, "
> -                     "but KVM does not support this memory backing");
> -        return -EINVAL;
> +    if (kvm_vm_enable_cap(kvm_state, KVM_CAP_S390_HPAGE_1M, 0)) {
> +        error_setg(errp, "Memory backing with 1M pages was specified, "
> +                   "but KVM does not support this memory backing");
> +        return;
>      }
>  
>      cap_hpage_1m = 1;
> -    return 0;
>  }
>  
>  int kvm_arch_init(MachineState *ms, KVMState *s)
>  {
>      MachineClass *mc = MACHINE_GET_CLASS(ms);
>  
> -    if (kvm_s390_configure_mempath_backing(s)) {
> -        return -EINVAL;
> -    }
> -
>      mc->default_cpu_type = S390_CPU_TYPE_NAME("host");
>      cap_sync_regs = kvm_check_extension(s, KVM_CAP_SYNC_REGS);
>      cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
> diff --git a/target/s390x/kvm_s390x.h b/target/s390x/kvm_s390x.h
> index 6e52287da3..caf985955b 100644
> --- a/target/s390x/kvm_s390x.h
> +++ b/target/s390x/kvm_s390x.h
> @@ -36,6 +36,7 @@ int kvm_s390_cmma_active(void);
>  void kvm_s390_cmma_reset(void);
>  void kvm_s390_reset_vcpu(S390CPU *cpu);
>  int kvm_s390_set_mem_limit(uint64_t new_limit, uint64_t *hw_limit);
> +void kvm_s390_set_max_pagesize(uint64_t pagesize, Error **errp);
>  void kvm_s390_crypto_reset(void);
>  void kvm_s390_restart_interrupt(S390CPU *cpu);
>  void kvm_s390_stop_interrupt(S390CPU *cpu);