On 07/09/15 00:42, Bandan Das wrote:
>
> If a Linux guest is assigned more memory than is supported
> by the host processor, the guest is unable to boot. That
> is expected, however, there's no message indicating the user
> what went wrong. This change prints a message to stderr if
> KVM has the corresponding capability.
>
> Reported-by: Laszlo Ersek <lersek@xxxxxxxxxx>
> Signed-off-by: Bandan Das <bsd@xxxxxxxxxx>
> ---
> linux-headers/linux/kvm.h | 1 +
> target-i386/kvm.c | 6 ++++++
> 2 files changed, 7 insertions(+)
>
> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> index 3bac873..6afad49 100644
> --- a/linux-headers/linux/kvm.h
> +++ b/linux-headers/linux/kvm.h
> @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info {
> #define KVM_CAP_DISABLE_QUIRKS 116
> #define KVM_CAP_X86_SMM 117
> #define KVM_CAP_MULTI_ADDRESS_SPACE 118
> +#define KVM_CAP_PHY_ADDR_WIDTH 119
>
> #ifdef KVM_CAP_IRQ_ROUTING
>
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 066d03d..66e3448 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> uint64_t shadow_mem;
> int ret;
> struct utsname utsname;
> + int max_phys_bits;
>
> ret = kvm_get_supported_msrs(s);
> if (ret < 0) {
> @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> }
> }
>
> + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH);
> + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size)
> + fprintf(stderr, "Warning: The amount of memory assigned to the guest "
> + "is more than that supported by the host CPU(s). Guest may be unstable.\n");
> +
> if (kvm_check_extension(s, KVM_CAP_X86_SMM)) {
> smram_machine_done.notify = register_smram_listener;
> qemu_add_machine_init_done_notifier(&smram_machine_done);
>
First, see my comments on the KVM patch.
Second, ram_size is not the right thing to compare. What should be
checked is whether the highest guest-physical address that maps to RAM
can be represented in the address width of the host processor (and only
if EPT is enabled, but that sub-condition belongs to the KVM patch).
Note that this is not the same as the check written in the patch. For
example, if you assume a 32-bit PCI hole with size 1 GB, then a total
guest RAM of size 63 GB will result in the highest guest-phys memory
address being 0xF_FFFF_FFFF, which just fits into 36 bits.
Correspondingly, the above code would not print the warning for
-m $((63 * 1024 + 1))
on my laptop (which has "address sizes : 36 bits physical, ..."), even
though such a guest would not boot for me (with EPT enabled).
Please see
http://thread.gmane.org/gmane.comp.bios.tianocore.devel/15418/focus=15447
So, "ram_size" in the controlling expression should be replaced with
"maximum_guest_ram_address" (which should be inclusive, and the <= relop
should be preserved).
Thanks
Laszlo
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