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KVM: selftests: Restore assert for non-nested VMs in access tracking test

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Restore the assert (on x86-64) that <10% of pages are still idle when NOT
running as a nested VM in the access tracking test.  The original assert
was converted to a "warning" to avoid false failures when running the
test in a VM, but the non-nested case does not suffer from the same
"infinite TLB size" issue.

Using the HYPERVISOR flag isn't infallible as VMMs aren't strictly
required to enumerate the "feature" in CPUID, but practically speaking
anyone that is running KVM selftests in VMs is going to be using a VMM
and hypervisor that sets the HYPERVISOR flag.

Cc: David Matlack <dmatlack@google.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221129175300.4052283-3-seanjc@google.com
This commit is contained in:
Sean Christopherson 2022-11-29 17:53:00 +00:00
parent a33004e844
commit 8fcee04213
2 changed files with 13 additions and 5 deletions
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17
tools/testing/selftests/kvm/access_tracking_perf_test.c
View file

@ -46,6 +46,7 @@
#include "test_util.h"
#include "memstress.h"
#include "guest_modes.h"
#include "processor.h"
/* Global variable used to synchronize all of the vCPU threads. */
static int iteration;
@ -180,15 +181,21 @@ static void mark_vcpu_memory_idle(struct kvm_vm *vm,
* access tracking but low enough as to not make the test too brittle
* over time and across architectures.
*
* Note that when run in nested virtualization, this check will trigger
* much more frequently because TLB size is unlimited and since no flush
* happens, much more pages are cached there and guest won't see the
* "idle" bit cleared.
* When running the guest as a nested VM, "warn" instead of asserting
* as the TLB size is effectively unlimited and the KVM doesn't
* explicitly flush the TLB when aging SPTEs. As a result, more pages
* are cached and the guest won't see the "idle" bit cleared.
*/
if (still_idle >= pages / 10)
if (still_idle >= pages / 10) {
#ifdef __x86_64__
TEST_ASSERT(this_cpu_has(X86_FEATURE_HYPERVISOR),
"vCPU%d: Too many pages still idle (%lu out of %lu)",
vcpu_idx, still_idle, pages);
#endif
printf("WARNING: vCPU%d: Too many pages still idle (%lu out of %lu), "
"this will affect performance results.\n",
vcpu_idx, still_idle, pages);
}
close(page_idle_fd);
close(pagemap_fd);

1
tools/testing/selftests/kvm/include/x86_64/processor.h
View file

@ -94,6 +94,7 @@ struct kvm_x86_cpu_feature {
#define X86_FEATURE_XSAVE KVM_X86_CPU_FEATURE(0x1, 0, ECX, 26)
#define X86_FEATURE_OSXSAVE KVM_X86_CPU_FEATURE(0x1, 0, ECX, 27)
#define X86_FEATURE_RDRAND KVM_X86_CPU_FEATURE(0x1, 0, ECX, 30)
#define X86_FEATURE_HYPERVISOR KVM_X86_CPU_FEATURE(0x1, 0, ECX, 31)
#define X86_FEATURE_PAE KVM_X86_CPU_FEATURE(0x1, 0, EDX, 6)
#define X86_FEATURE_MCE KVM_X86_CPU_FEATURE(0x1, 0, EDX, 7)
#define X86_FEATURE_APIC KVM_X86_CPU_FEATURE(0x1, 0, EDX, 9)