On 2023/12/13 下午3:15, zhaotianrui wrote:
在 2023/12/13 上午1:18, Sean Christopherson 写道:
On Tue, Dec 12, 2023, zhaotianrui wrote:
Hi, Sean:
I want to change the definition of DEFAULT_GUEST_TEST_MEM in the common
file "memstress.h", like this:
/* Default guest test virtual memory offset */
+#ifndef DEFAULT_GUEST_TEST_MEM
#define DEFAULT_GUEST_TEST_MEM 0xc0000000
+#endif
As this address should be re-defined in LoongArch headers.
Why? E.g. is 0xc0000000 unconditionally reserved, not guaranteed to
be valid,
something else?
So, do you have any suggesstion?
Hmm, I think ideally kvm_util_base.h would define a range of memory
that can be
used by tests for arbitrary data. Multiple tests use 0xc0000000,
which is not
entirely arbitrary, i.e. it doesn't _need_ to be 0xc0000000, but
0xc0000000 is
convenient because it's 32-bit addressable and doesn't overlap
reserved areas in
other architectures.
In general text entry address of user application on x86/arm64 Linux
is 0x200000, however on LoongArch system text entry address is strange,
its value 0x120000000.
When DEFAULT_GUEST_TEST_MEM is defined as 0xc0000000, there is
limitation for guest memory size, it cannot exceed 0x120000000 -
0xc000000 = 1.5G bytes, else there will be conflict. However
there is no such issue on x86/arm64, since 0xc0000000 is above text
entry address 0x200000.
The LoongArch link scripts actually is strange, it brings out some
compatible issues such dpdk/kvm selftest when user applications
want fixed virtual address space.
So here DEFAULT_GUEST_TEST_MEM is defined as 0x130000000 separately,
maybe 0x140000000 is better since it is 1G super-page aligned for 4K
page size.
Regards
Bibo Mao
Thanks for your explanation, and LoongArch want to define
DEFAULT_GUEST_TEST_MEM to 0x130000000. As default base address for
application loading is 0x120000000, DEFAULT_GUEST_TEST_MEM should be
larger than app loading address, so that PER_VCPU_MEM_SIZE can be large
enough, and kvm selftests app size is smaller than 256M in generic.
Thanks
Tianrui Zhao
