Jens Freimann wrote:
> From: Christian Borntraeger <borntrae...@de.ibm.com>
>
> By default qemu will use MAP_PRIVATE for guest pages. This will write
> protect pages and thus break on s390 systems that dont support this feature.
> Therefore qemu has a hack to always use MAP_SHARED for s390. But MAP_SHARED
> has other problems (no dirty pages tracking, a lot more swap overhead etc.)
> Newer systems allow the distinction via KVM_CAP_S390_COW. With this feature
> qemu can use the standard qemu alloc if available, otherwise it will use
> the old s390 hack.
>
> Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
> Signed-off-by: Jens Freimann <jf...@linux.vnet.ibm.com>
> ---
> exec.c | 54
> +++++++++++++++++++++++++++++++++++++---------------
> kvm.h | 9 +++++++++
> oslib-posix.c | 3 +++
> target-s390x/kvm.c | 6 ++++++
> 4 files changed, 57 insertions(+), 15 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index a0494c7..8fec680 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2618,6 +2618,43 @@ void qemu_ram_set_idstr(ram_addr_t addr, const char
> *name, DeviceState *dev)
> }
> }
>
> +/*
> + * lets make sure that we dont have the old s390x limitations regarding
> + * guest mappings
> + */
> +static int legacy_s390x_mem_layout(void)
> +{
> +#if defined(TARGET_S390X)
> + return kvm_has_legacy_s390x_memlayout();
> +#else
> + return 0;
> +#endif
> +}
> +
> +/*
> + * Legacy layout for s390:
> + * Older S390 KVM requires the topmost vma of the RAM to be
> + * smaller than an system defined value, which is at least 256GB.
> + * Larger systems have larger values. We put the guest between
> + * the end of data segment (system break) and this value. We
> + * use 32GB as a base to have enough room for the system break
> + * to grow. We also have to use MAP parameters that avoid
> + * read-only mapping of guest pages.
> + */
> +static void *legacy_s390_alloc(ram_addr_t size)
> +{
> + void *mem;
> +
> + mem = mmap((void *) 0x800000000ULL, size,
> + PROT_EXEC|PROT_READ|PROT_WRITE,
> + MAP_SHARED | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
> + if (mem == MAP_FAILED) {
> + fprintf(stderr, "Allocating RAM failed\n");
> + abort();
> + }
> + return mem;
> +}
> +
>
Is there any way we can move the above code to target-s390x? Having the
branch below is already invasive enough for generic code, but we really
don't need all the special s390 quirks to live here.
> ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
> MemoryRegion *mr)
> {
> @@ -2644,26 +2681,13 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size,
> void *host,
> exit(1);
> #endif
> } else {
> -#if defined(TARGET_S390X) && defined(CONFIG_KVM)
> - /* S390 KVM requires the topmost vma of the RAM to be smaller
> than
> - an system defined value, which is at least 256GB. Larger
> systems
> - have larger values. We put the guest between the end of data
> - segment (system break) and this value. We use 32GB as a base
> to
> - have enough room for the system break to grow. */
> - new_block->host = mmap((void*)0x800000000, size,
> - PROT_EXEC|PROT_READ|PROT_WRITE,
> - MAP_SHARED | MAP_ANONYMOUS | MAP_FIXED,
> -1, 0);
> - if (new_block->host == MAP_FAILED) {
> - fprintf(stderr, "Allocating RAM failed\n");
> - abort();
> - }
> -#else
> if (xen_enabled()) {
> xen_ram_alloc(new_block->offset, size, mr);
>
#ifdef TARGET_S390X
> + } else if (legacy_s390x_mem_layout()) {
> + new_block->host = legacy_s390_alloc(size);
>
#endif
maybe? That way you could move everything to target-s390x.
> } else {
> new_block->host = qemu_vmalloc(size);
> }
> -#endif
> qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
> }
> }
> diff --git a/kvm.h b/kvm.h
> index 9c7b0ea..ca0557e 100644
> --- a/kvm.h
> +++ b/kvm.h
> @@ -62,6 +62,15 @@ int kvm_has_pit_state2(void);
> int kvm_has_many_ioeventfds(void);
> int kvm_has_gsi_routing(void);
>
> +#ifndef CONFIG_KVM
> +static inline int kvm_has_legacy_s390x_memlayout(void)
>
An s390 function in generic kvm.h? No way :)
> +{
> + return 0;
> +}
> +#else
> +int kvm_has_legacy_s390x_memlayout(void);
> +#endif
> +
> int kvm_allows_irq0_override(void);
>
> #ifdef NEED_CPU_H
> diff --git a/oslib-posix.c b/oslib-posix.c
> index b6a3c7f..93902ac 100644
> --- a/oslib-posix.c
> +++ b/oslib-posix.c
> @@ -41,6 +41,9 @@ extern int daemon(int, int);
> therefore we need special code which handles running on Valgrind. */
> # define QEMU_VMALLOC_ALIGN (512 * 4096)
> # define CONFIG_VALGRIND
> +#elif defined(__linux__) && defined(__s390x__)
> + /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
> +# define QEMU_VMALLOC_ALIGN (256 * 4096)
> #else
> # define QEMU_VMALLOC_ALIGN getpagesize()
> #endif
> diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c
> index 90aad61..93a8431 100644
> --- a/target-s390x/kvm.c
> +++ b/target-s390x/kvm.c
> @@ -135,6 +135,12 @@ int kvm_arch_get_registers(CPUS390XState *env)
> return 0;
> }
>
> +int kvm_has_legacy_s390x_memlayout(void)
> +{
> + return !kvm_check_extension(kvm_state, KVM_CAP_S390_GMAP) ||
> + !kvm_check_extension(kvm_state, KVM_CAP_S390_COW);
> +}
> +
> int kvm_arch_insert_sw_breakpoint(CPUS390XState *env, struct
> kvm_sw_breakpoint *bp)
> {
> static const uint8_t diag_501[] = {0x83, 0x24, 0x05, 0x01};
>
