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Date: Tue, 12 Apr 2022 15:11:28 -0700
From: Ben Gardon <bgardon@...gle.com>
To: David Matlack <dmatlack@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
kvm list <kvm@...r.kernel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Peter Xu <peterx@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Peter Shier <pshier@...gle.com>,
David Dunn <daviddunn@...gle.com>,
Junaid Shahid <junaids@...gle.com>,
Jim Mattson <jmattson@...gle.com>,
Mingwei Zhang <mizhang@...gle.com>,
Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH v4 05/10] KVM: selftests: Add NX huge pages test
On Mon, Apr 11, 2022 at 3:28 PM David Matlack <dmatlack@...gle.com> wrote:
>
> On Mon, Apr 11, 2022 at 2:10 PM Ben Gardon <bgardon@...gle.com> wrote:
> >
> > There's currently no test coverage of NX hugepages in KVM selftests, so
> > add a basic test to ensure that the feature works as intended.
> >
> > Signed-off-by: Ben Gardon <bgardon@...gle.com>
> > ---
> > tools/testing/selftests/kvm/Makefile | 10 ++
> > .../selftests/kvm/include/kvm_util_base.h | 1 +
> > tools/testing/selftests/kvm/lib/kvm_util.c | 48 ++++++
> > .../selftests/kvm/x86_64/nx_huge_pages_test.c | 163 ++++++++++++++++++
> > .../kvm/x86_64/nx_huge_pages_test.sh | 25 +++
> > 5 files changed, 247 insertions(+)
> > create mode 100644 tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > create mode 100755 tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> >
> > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> > index af582d168621..9bb9bce4df37 100644
> > --- a/tools/testing/selftests/kvm/Makefile
> > +++ b/tools/testing/selftests/kvm/Makefile
> > @@ -43,6 +43,10 @@ LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c lib/aarch64/handler
> > LIBKVM_s390x = lib/s390x/processor.c lib/s390x/ucall.c lib/s390x/diag318_test_handler.c
> > LIBKVM_riscv = lib/riscv/processor.c lib/riscv/ucall.c
> >
> > +# Non-compiled test targets
> > +TEST_PROGS_x86_64 += x86_64/nx_huge_pages_test.sh
> > +
> > +# Compiled test targets
> > TEST_GEN_PROGS_x86_64 = x86_64/cpuid_test
> > TEST_GEN_PROGS_x86_64 += x86_64/cr4_cpuid_sync_test
> > TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
> > @@ -104,6 +108,9 @@ TEST_GEN_PROGS_x86_64 += steal_time
> > TEST_GEN_PROGS_x86_64 += kvm_binary_stats_test
> > TEST_GEN_PROGS_x86_64 += system_counter_offset_test
> >
> > +# Compiled outputs used by test targets
> > +TEST_GEN_PROGS_EXTENDED_x86_64 += x86_64/nx_huge_pages_test
> > +
> > TEST_GEN_PROGS_aarch64 += aarch64/arch_timer
> > TEST_GEN_PROGS_aarch64 += aarch64/debug-exceptions
> > TEST_GEN_PROGS_aarch64 += aarch64/get-reg-list
> > @@ -142,7 +149,9 @@ TEST_GEN_PROGS_riscv += kvm_page_table_test
> > TEST_GEN_PROGS_riscv += set_memory_region_test
> > TEST_GEN_PROGS_riscv += kvm_binary_stats_test
> >
> > +TEST_PROGS += $(TEST_PROGS_$(UNAME_M))
> > TEST_GEN_PROGS += $(TEST_GEN_PROGS_$(UNAME_M))
> > +TEST_GEN_PROGS_EXTENDED += $(TEST_GEN_PROGS_EXTENDED_$(UNAME_M))
> > LIBKVM += $(LIBKVM_$(UNAME_M))
> >
> > INSTALL_HDR_PATH = $(top_srcdir)/usr
> > @@ -193,6 +202,7 @@ $(OUTPUT)/libkvm.a: $(LIBKVM_OBJS)
> > x := $(shell mkdir -p $(sort $(dir $(TEST_GEN_PROGS))))
> > all: $(STATIC_LIBS)
> > $(TEST_GEN_PROGS): $(STATIC_LIBS)
> > +$(TEST_GEN_PROGS_EXTENDED): $(STATIC_LIBS)
> >
> > cscope: include_paths = $(LINUX_TOOL_INCLUDE) $(LINUX_HDR_PATH) include lib ..
> > cscope:
> > diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> > index b2684cfc2cb1..f9c2ac0a5b97 100644
> > --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> > +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> > @@ -408,6 +408,7 @@ void read_vm_stats_desc(int stats_fd, struct kvm_stats_header *header,
> > int read_stat_data(int stats_fd, struct kvm_stats_header *header,
> > struct kvm_stats_desc *desc, uint64_t *data,
> > ssize_t max_elements);
> > +uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name);
> >
> > uint32_t guest_get_vcpuid(void);
> >
> > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> > index 64e2085f1129..833c7e63d62d 100644
> > --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > @@ -2614,3 +2614,51 @@ int read_stat_data(int stats_fd, struct kvm_stats_header *header,
> >
> > return ret;
> > }
> > +
> > +static int vm_get_stat_data(struct kvm_vm *vm, const char *stat_name,
> > + uint64_t *data, ssize_t max_elements)
> > +{
> > + struct kvm_stats_desc *stats_desc;
> > + struct kvm_stats_header header;
> > + struct kvm_stats_desc *desc;
> > + size_t size_desc;
> > + int stats_fd;
> > + int ret = -EINVAL;
> > + int i;
> > +
> > + stats_fd = vm_get_stats_fd(vm);
> > +
> > + read_vm_stats_header(stats_fd, &header);
> > +
> > + stats_desc = alloc_vm_stats_desc(stats_fd, &header);
> > + read_vm_stats_desc(stats_fd, &header, stats_desc);
>
> This is a fair bit of redundant work to do when reading every stat.
> Reading stats in selftests is probably not going to be
> performance-senstive, but it should be pretty easy to move everything
> above to VM initialization and storing the outputs in struct kvm_vm
> for access during this function.
>
That's true, but for now I'm just going to leave this as-is. If we
have a case where it is performance sensitive, we can look at
optimizing the stats collection for that case.
> > +
> > + size_desc = sizeof(struct kvm_stats_desc) + header.name_size;
> > +
> > + /* Read kvm stats data one by one */
> > + for (i = 0; i < header.num_desc; ++i) {
> > + desc = (void *)stats_desc + (i * size_desc);
> > +
> > + if (strcmp(desc->name, stat_name))
> > + continue;
> > +
> > + ret = read_stat_data(stats_fd, &header, desc, data,
> > + max_elements);
> > + }
> > +
> > + free(stats_desc);
> > + close(stats_fd);
> > + return ret;
> > +}
> > +
> > +uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name)
>
> nit: I'd prefer the simpler "vm_get_stat()". The function signature
> already makes it clear we're reading one stat value. And when we add
> more support for more complicated stats (e.g.
> vm_get_histogram_stat()), I think "vm_get_stat()" will still work for
> reading single value stats.
Will do.
>
> > +{
> > + uint64_t data;
> > + int ret;
> > +
> > + ret = vm_get_stat_data(vm, stat_name, &data, 1);
> > + TEST_ASSERT(ret == 1,
> > + "Stat %s expected to have 1 element, but %d returned",
> > + stat_name, ret);
> > + return data;
> > +}
> > diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > new file mode 100644
> > index 000000000000..3f21726b22c7
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
> > @@ -0,0 +1,163 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * tools/testing/selftests/kvm/nx_huge_page_test.c
> > + *
> > + * Usage: to be run via nx_huge_page_test.sh, which does the necessary
> > + * environment setup and teardown
> > + *
> > + * Copyright (C) 2022, Google LLC.
> > + */
> > +
> > +#define _GNU_SOURCE
> > +
> > +#include <fcntl.h>
> > +#include <stdint.h>
> > +#include <time.h>
> > +
> > +#include <test_util.h>
> > +#include "kvm_util.h"
> > +
> > +#define HPAGE_SLOT 10
> > +#define HPAGE_GVA (23*1024*1024)
> > +#define HPAGE_GPA (10*1024*1024)
> > +#define HPAGE_SLOT_NPAGES (512 * 3)
> > +#define PAGE_SIZE 4096
> > +
> > +/*
> > + * When writing to guest memory, write the opcode for the `ret` instruction so
> > + * that subsequent iteractions can exercise instruction fetch by calling the
> > + * memory.
>
> I think this comment needs to be reworded to better fit this test.
>
Woops, will do.
>
> > + */
> > +#define RETURN_OPCODE 0xC3
> > +
> > +void guest_code(void)
> > +{
> > + uint64_t hpage_1 = HPAGE_GVA;
> > + uint64_t hpage_2 = hpage_1 + (PAGE_SIZE * 512);
> > + uint64_t hpage_3 = hpage_2 + (PAGE_SIZE * 512);
> > +
> > + READ_ONCE(*(uint64_t *)hpage_1);
> > + GUEST_SYNC(1);
> > +
> > + READ_ONCE(*(uint64_t *)hpage_2);
> > + GUEST_SYNC(2);
> > +
> > + ((void (*)(void)) hpage_1)();
> > + GUEST_SYNC(3);
> > +
> > + ((void (*)(void)) hpage_3)();
> > + GUEST_SYNC(4);
> > +
> > + READ_ONCE(*(uint64_t *)hpage_1);
> > + GUEST_SYNC(5);
> > +
> > + READ_ONCE(*(uint64_t *)hpage_3);
> > + GUEST_SYNC(6);
> > +}
> > +
> > +static void check_2m_page_count(struct kvm_vm *vm, int expected_pages_2m)
> > +{
> > + int actual_pages_2m;
> > +
> > + actual_pages_2m = vm_get_single_stat(vm, "pages_2m");
> > +
> > + TEST_ASSERT(actual_pages_2m == expected_pages_2m,
> > + "Unexpected 2m page count. Expected %d, got %d",
> > + expected_pages_2m, actual_pages_2m);
> > +}
> > +
> > +static void check_split_count(struct kvm_vm *vm, int expected_splits)
> > +{
> > + int actual_splits;
> > +
> > + actual_splits = vm_get_single_stat(vm, "nx_lpage_splits");
> > +
> > + TEST_ASSERT(actual_splits == expected_splits,
> > + "Unexpected nx lpage split count. Expected %d, got %d",
> > + expected_splits, actual_splits);
> > +}
> > +
> > +int main(int argc, char **argv)
> > +{
> > + struct kvm_vm *vm;
> > + struct timespec ts;
> > + void *hva;
> > +
> > + vm = vm_create_default(0, 0, guest_code);
> > +
> > + vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS_HUGETLB,
> > + HPAGE_GPA, HPAGE_SLOT,
> > + HPAGE_SLOT_NPAGES, 0);
> > +
> > + virt_map(vm, HPAGE_GVA, HPAGE_GPA, HPAGE_SLOT_NPAGES);
> > +
> > + hva = addr_gpa2hva(vm, HPAGE_GPA);
> > + memset(hva, RETURN_OPCODE, HPAGE_SLOT_NPAGES * PAGE_SIZE);
> > +
> > + check_2m_page_count(vm, 0);
> > + check_split_count(vm, 0);
> > +
> > + /*
> > + * The guest code will first read from the first hugepage, resulting
> > + * in a huge page mapping being created.
> > + */
> > + vcpu_run(vm, 0);
> > + check_2m_page_count(vm, 1);
> > + check_split_count(vm, 0);
> > +
> > + /*
> > + * Then the guest code will read from the second hugepage, resulting
> > + * in another huge page mapping being created.
> > + */
> > + vcpu_run(vm, 0);
> > + check_2m_page_count(vm, 2);
> > + check_split_count(vm, 0);
> > +
> > + /*
> > + * Next, the guest will execute from the first huge page, causing it
> > + * to be remapped at 4k.
> > + */
> > + vcpu_run(vm, 0);
> > + check_2m_page_count(vm, 1);
> > + check_split_count(vm, 1);
> > +
> > + /*
> > + * Executing from the third huge page (previously unaccessed) will
> > + * cause part to be mapped at 4k.
> > + */
> > + vcpu_run(vm, 0);
> > + check_2m_page_count(vm, 1);
> > + check_split_count(vm, 2);
> > +
> > + /* Reading from the first huge page again should have no effect. */
> > + vcpu_run(vm, 0);
> > + check_2m_page_count(vm, 1);
> > + check_split_count(vm, 2);
> > +
> > + /*
> > + * Give recovery thread time to run. The wrapper script sets
> > + * recovery_period_ms to 100, so wait 5x that.
> > + */
> > + ts.tv_sec = 0;
> > + ts.tv_nsec = 500000000;
> > + nanosleep(&ts, NULL);
> > +
> > + /*
> > + * Now that the reclaimer has run, all the split pages should be gone.
> > + */
> > + check_2m_page_count(vm, 1);
> > + check_split_count(vm, 0);
> > +
> > + /*
> > + * The 4k mapping on hpage 3 should have been removed, so check that
> > + * reading from it causes a huge page mapping to be installed.
> > + */
> > + vcpu_run(vm, 0);
> > + check_2m_page_count(vm, 2);
> > + check_split_count(vm, 0);
> > +
> > + kvm_vm_free(vm);
> > +
> > + return 0;
> > +}
> > +
> > diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> > new file mode 100755
> > index 000000000000..19fc95723fcb
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
> > @@ -0,0 +1,25 @@
> > +#!/bin/bash
> > +# SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +# tools/testing/selftests/kvm/nx_huge_page_test.sh
> > +# Copyright (C) 2022, Google LLC.
> > +
> > +NX_HUGE_PAGES=$(cat /sys/module/kvm/parameters/nx_huge_pages)
> > +NX_HUGE_PAGES_RECOVERY_RATIO=$(cat /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio)
> > +NX_HUGE_PAGES_RECOVERY_PERIOD=$(cat /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms)
> > +HUGE_PAGES=$(cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages)
> > +
> > +echo 1 > /sys/module/kvm/parameters/nx_huge_pages
> > +echo 1 > /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio
> > +echo 100 > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
> > +echo 200 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> > +
> > +./nx_huge_pages_test
> > +RET=$?
> > +
> > +echo $NX_HUGE_PAGES > /sys/module/kvm/parameters/nx_huge_pages
> > +echo $NX_HUGE_PAGES_RECOVERY_RATIO > /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio
> > +echo $NX_HUGE_PAGES_RECOVERY_PERIOD > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
> > +echo $HUGE_PAGES > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> > +
> > +exit $RET
> > --
> > 2.35.1.1178.g4f1659d476-goog
> >
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