On Mon, 16 May 2022 16:55:16 +0100
Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote:
> The user can specify the virtual machine memory size in MB, which is saved
> in cfg->ram_size. kvmtool validates it against the host memory size,
> converted from bytes to MB. ram_size is then converted to bytes, and this
> is how it is used throughout the rest of kvmtool.
>
> To avoid any confusion about the unit of measurement, especially once the
> user is allowed to specify the unit of measurement, always use ram_size in
> bytes.
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
> builtin-run.c | 19 ++++++++++---------
> include/kvm/kvm-config.h | 7 ++++---
> include/kvm/kvm.h | 2 +-
> 3 files changed, 15 insertions(+), 13 deletions(-)
>
> diff --git a/builtin-run.c b/builtin-run.c
> index 0126c9fbcba6..236c59d2f86f 100644
> --- a/builtin-run.c
> +++ b/builtin-run.c
> @@ -36,6 +36,7 @@
>
> #include <linux/types.h>
> #include <linux/err.h>
> +#include <linux/sizes.h>
>
> #include <sys/utsname.h>
> #include <sys/types.h>
> @@ -264,7 +265,7 @@ static u64 host_ram_size(void)
> return 0;
> }
>
> - return (nr_pages * page_size) >> MB_SHIFT;
> + return nr_pages * page_size;
So while looking for potential overflows on 32-bit systems, I realised
that this was already broken: On my Calxeda Highbank (arm32) with 8GB of
memory, this returns a negative number, because of the signed longs.
Can you cast nr_pages to u64 while at it, to fix that? I don't think we
need a separate patch for that ...
> }
>
> /*
> @@ -278,11 +279,11 @@ static u64 get_ram_size(int nr_cpus)
> u64 available;
> u64 ram_size;
>
> - ram_size = 64 * (nr_cpus + 3);
> + ram_size = SZ_64M * (nr_cpus + 3);
This overflows on 32-bit system starting with 29 vCPUs. If you use "3ULL",
this problem goes away.
Cheers,
Andre
>
> available = host_ram_size() * RAM_SIZE_RATIO;
> if (!available)
> - available = MIN_RAM_SIZE_MB;
> + available = MIN_RAM_SIZE;
>
> if (ram_size > available)
> ram_size = available;
> @@ -595,13 +596,13 @@ static struct kvm *kvm_cmd_run_init(int argc, const char **argv)
>
> if (!kvm->cfg.ram_size)
> kvm->cfg.ram_size = get_ram_size(kvm->cfg.nrcpus);
> + else
> + kvm->cfg.ram_size <<= MB_SHIFT;
>
> if (kvm->cfg.ram_size > host_ram_size())
> pr_warning("Guest memory size %lluMB exceeds host physical RAM size %lluMB",
> - (unsigned long long)kvm->cfg.ram_size,
> - (unsigned long long)host_ram_size());
> -
> - kvm->cfg.ram_size <<= MB_SHIFT;
> + (unsigned long long)kvm->cfg.ram_size >> MB_SHIFT,
> + (unsigned long long)host_ram_size() >> MB_SHIFT);
>
> if (!kvm->cfg.dev)
> kvm->cfg.dev = DEFAULT_KVM_DEV;
> @@ -676,12 +677,12 @@ static struct kvm *kvm_cmd_run_init(int argc, const char **argv)
> if (kvm->cfg.kernel_filename) {
> printf(" # %s run -k %s -m %Lu -c %d --name %s\n", KVM_BINARY_NAME,
> kvm->cfg.kernel_filename,
> - (unsigned long long)kvm->cfg.ram_size / 1024 / 1024,
> + (unsigned long long)kvm->cfg.ram_size >> MB_SHIFT,
> kvm->cfg.nrcpus, kvm->cfg.guest_name);
> } else if (kvm->cfg.firmware_filename) {
> printf(" # %s run --firmware %s -m %Lu -c %d --name %s\n", KVM_BINARY_NAME,
> kvm->cfg.firmware_filename,
> - (unsigned long long)kvm->cfg.ram_size / 1024 / 1024,
> + (unsigned long long)kvm->cfg.ram_size >> MB_SHIFT,
> kvm->cfg.nrcpus, kvm->cfg.guest_name);
> }
>
> diff --git a/include/kvm/kvm-config.h b/include/kvm/kvm-config.h
> index 6a5720c4c7d4..31bc89520d52 100644
> --- a/include/kvm/kvm-config.h
> +++ b/include/kvm/kvm-config.h
> @@ -5,6 +5,8 @@
> #include "kvm/vfio.h"
> #include "kvm/kvm-config-arch.h"
>
> +#include <linux/sizes.h>
> +
> #define DEFAULT_KVM_DEV "/dev/kvm"
> #define DEFAULT_CONSOLE "serial"
> #define DEFAULT_NETWORK "user"
> @@ -15,14 +17,13 @@
> #define DEFAULT_SCRIPT "none"
> #define DEFAULT_SANDBOX_FILENAME "guest/sandbox.sh"
>
> -#define MIN_RAM_SIZE_MB (64ULL)
> -#define MIN_RAM_SIZE_BYTE (MIN_RAM_SIZE_MB << MB_SHIFT)
> +#define MIN_RAM_SIZE SZ_64M
>
> struct kvm_config {
> struct kvm_config_arch arch;
> struct disk_image_params disk_image[MAX_DISK_IMAGES];
> struct vfio_device_params *vfio_devices;
> - u64 ram_size;
> + u64 ram_size; /* Guest memory size, in bytes */
> u8 num_net_devices;
> u8 num_vfio_devices;
> u64 vsock_cid;
> diff --git a/include/kvm/kvm.h b/include/kvm/kvm.h
> index ad732e56f5ed..7b14b33b50ca 100644
> --- a/include/kvm/kvm.h
> +++ b/include/kvm/kvm.h
> @@ -87,7 +87,7 @@ struct kvm {
> struct kvm_cpu **cpus;
>
> u32 mem_slots; /* for KVM_SET_USER_MEMORY_REGION */
> - u64 ram_size;
> + u64 ram_size; /* Guest memory size, in bytes */
> void *ram_start;
> u64 ram_pagesize;
> struct mutex mem_banks_lock;
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