Re: [kvm-unit-tests PATCH v2] x86/asyncpf: fix async page fault issues

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On 12/25/2023 9:51 AM, Xiaoyao Li wrote:
On 12/18/2023 3:14 PM, Dan Wu wrote:
KVM switched to use interrupt for 'page ready' APF event since Linux v5.10 and the legacy mechanism using #PF was deprecated. Interrupt-based 'page-ready'
notification required KVM_ASYNC_PF_DELIVERY_AS_INT to be set as well in
MSR_KVM_ASYNC_PF_EN to enable asyncpf.

This patch tries to update asyncpf.c for the new interrupt-based notification.

please avoid using 'This patch', and just use imperative mood.
thanks for your suggestion.

It checks (KVM_FEATURE_ASYNC_PF && KVM_FEATURE_ASYNC_PF_INT) and implements
interrupt-based 'page-ready' handler.

To run this test, add the QEMU option "-cpu host" to check CPUID, since
KVM_FEATURE_ASYNC_PF_INT can't be detected without "-cpu host".

Update the usage of how to setup cgroup for different cgroup versions.

Signed-off-by: Dan Wu <dan1.wu@xxxxxxxxx>

This patch looks good to me, apart from some nits above and below.
OK, I will modify them in the next version. Thanks for your review.

Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>

---
The test is based on asyncpf.c and simplifies implementation by reducing the memory
access round from 2 to 1.

v2:
- removed asyncpf_int.c and asyncpf.h and modified asyncpf.c to use ASYNC_PF_INT.
---
  lib/x86/processor.h |   6 ++
  x86/asyncpf.c       | 152 +++++++++++++++++++++++++++-----------------
  x86/unittests.cfg   |   2 +-
  3 files changed, 101 insertions(+), 59 deletions(-)

diff --git a/lib/x86/processor.h b/lib/x86/processor.h
index 44f4fd1e..1a0f1243 100644
--- a/lib/x86/processor.h
+++ b/lib/x86/processor.h
@@ -263,6 +263,12 @@ static inline bool is_intel(void)
  #define    X86_FEATURE_ARCH_CAPABILITIES    (CPUID(0x7, 0, EDX, 29))
  #define    X86_FEATURE_PKS            (CPUID(0x7, 0, ECX, 31))
  +/*
+ * KVM defined leafs
+ */
+#define    KVM_FEATURE_ASYNC_PF        (CPUID(0x40000001, 0, EAX, 4))
+#define    KVM_FEATURE_ASYNC_PF_INT    (CPUID(0x40000001, 0, EAX, 14))
+
  /*
   * Extended Leafs, a.k.a. AMD defined
   */
diff --git a/x86/asyncpf.c b/x86/asyncpf.c
index bc515be9..8ae9ea40 100644
--- a/x86/asyncpf.c
+++ b/x86/asyncpf.c
@@ -1,111 +1,147 @@
  /*
   * Async PF test. For the test to actually do anything it needs to be started - * in memory cgroup with 512M of memory and with more then 1G memory provided + * in memory cgroup with 512M of memory and with more than 1G memory provided
   * to the guest.
   *
+ * To identify the cgroup version on Linux:
+ * stat -fc %T /sys/fs/cgroup/
+ *
+ * If the output is tmpfs, your system is using cgroup v1:
   * To create cgroup do as root:
   * mkdir /dev/cgroup
   * mount -t cgroup none -omemory /dev/cgroup
   * chmod a+rxw /dev/cgroup/
- *

keep this line is better, IMO.

   * From a shell you will start qemu from:
   * mkdir /dev/cgroup/1
   * echo $$ >  /dev/cgroup/1/tasks
   * echo 512M > /dev/cgroup/1/memory.limit_in_bytes
   *
+ * If the output is cgroup2fs, your system is using cgroup v2:
+ * mkdir /sys/fs/cgroup/cg1
+ * echo $$ >  /sys/fs/cgroup/cg1/cgroup.procs
+ * echo 512M > /sys/fs/cgroup/cg1/memory.max
+ *
   */
-#include "x86/msr.h"
  #include "x86/processor.h"
-#include "x86/apic-defs.h"
  #include "x86/apic.h"
-#include "x86/desc.h"
  #include "x86/isr.h"
  #include "x86/vm.h"
-
-#include "asm/page.h"
  #include "alloc.h"
-#include "libcflat.h"
  #include "vmalloc.h"
-#include <stdint.h>

maybe it deserves one line mentioning in the commit message, like "cleaning up the include headers"

  #define KVM_PV_REASON_PAGE_NOT_PRESENT 1
-#define KVM_PV_REASON_PAGE_READY 2
    #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
+#define MSR_KVM_ASYNC_PF_INT    0x4b564d06
+#define MSR_KVM_ASYNC_PF_ACK    0x4b564d07
    #define KVM_ASYNC_PF_ENABLED                    (1 << 0)
  #define KVM_ASYNC_PF_SEND_ALWAYS                (1 << 1)
+#define KVM_ASYNC_PF_DELIVERY_AS_INT            (1 << 3)
+
+#define HYPERVISOR_CALLBACK_VECTOR    0xf3
+
+struct kvm_vcpu_pv_apf_data {
+      /* Used for 'page not present' events delivered via #PF */
+      uint32_t  flags;
+
+      /* Used for 'page ready' events delivered via interrupt notification */
+      uint32_t  token;
+
+      uint8_t  pad[56];
+      uint32_t  enabled;
+} apf_reason __attribute__((aligned(64)));

as well, it deserves some words in commit message.

-volatile uint32_t apf_reason __attribute__((aligned(64)));
  char *buf;
+void* virt;
  volatile uint64_t  i;
  volatile uint64_t phys;
+volatile uint32_t saved_token;
+volatile uint32_t asyncpf_num;
  -static inline uint32_t get_apf_reason(void)
+static inline uint32_t get_and_clear_apf_reason(void)
  {
-    uint32_t r = apf_reason;
-    apf_reason = 0;
+    uint32_t r = apf_reason.flags;
+    apf_reason.flags = 0;
      return r;
  }
  -static void pf_isr(struct ex_regs *r)
+static void handle_interrupt(isr_regs_t *regs)
  {
-    void* virt = (void*)((ulong)(buf+i) & ~(PAGE_SIZE-1));
-    uint32_t reason = get_apf_reason();
+    uint32_t apf_token = apf_reason.token;
+
+    apf_reason.token = 0;
+    wrmsr(MSR_KVM_ASYNC_PF_ACK, 1);
+
+    if (apf_token == 0xffffffff) {
+        report_pass("Wakeup all, got token 0x%x", apf_token);
+    } else if (apf_token == saved_token) {
+        asyncpf_num++;
+        install_pte(phys_to_virt(read_cr3()), 1, virt, phys | PT_PRESENT_MASK | PT_WRITABLE_MASK, 0);
+        phys = 0;
+    } else {
+        report_fail("unexpected async pf int token 0x%x", apf_token);
+    }
+
+    eoi();
+}
  +static void handle_pf(struct ex_regs *r)
+{
+    virt = (void*)((ulong)(buf+i) & ~(PAGE_SIZE-1));
+    uint32_t reason = get_and_clear_apf_reason();
      switch (reason) {
-        case 0:
-            report_fail("unexpected #PF at %#lx", read_cr2());
-            break;
-        case KVM_PV_REASON_PAGE_NOT_PRESENT:
-            phys = virt_to_pte_phys(phys_to_virt(read_cr3()), virt);
-            install_pte(phys_to_virt(read_cr3()), 1, virt, phys, 0);
-            write_cr3(read_cr3());
-            report_pass("Got not present #PF token %lx virt addr %p phys addr %#" PRIx64,
-                    read_cr2(), virt, phys);
-            while(phys) {
-                safe_halt(); /* enables irq */
-                cli();
-            }
-            break;
-        case KVM_PV_REASON_PAGE_READY:
-            report_pass("Got present #PF token %lx", read_cr2());
-            if ((uint32_t)read_cr2() == ~0)
-                break;
-            install_pte(phys_to_virt(read_cr3()), 1, virt, phys | PT_PRESENT_MASK | PT_WRITABLE_MASK, 0);
-            write_cr3(read_cr3());
-            phys = 0;
-            break;
-        default:
-            report_fail("unexpected async pf reason %" PRId32, reason);
-            break;
+    case 0:
+        report_fail("unexpected #PF at %#lx", read_cr2());
+        exit(report_summary());
+    case KVM_PV_REASON_PAGE_NOT_PRESENT:
+        phys = virt_to_pte_phys(phys_to_virt(read_cr3()), virt);
+        install_pte(phys_to_virt(read_cr3()), 1, virt, phys, 0);
+        write_cr3(read_cr3());
+        saved_token = read_cr2();
+        while (phys) {
+            safe_halt(); /* enables irq */
+        }
+        break;
+    default:
+        report_fail("unexpected async pf with reason 0x%x", reason);
+        exit(report_summary());
      }
  }
  -#define MEM 1ull*1024*1024*1024
+#define MEM (1ull*1024*1024*1024)
    int main(int ac, char **av)
  {
-    int loop = 2;
+    if (!this_cpu_has(KVM_FEATURE_ASYNC_PF)) {
+        report_skip("KVM_FEATURE_ASYNC_PF is not supported\n");
+        return report_summary();
+    }
+
+    if (!this_cpu_has(KVM_FEATURE_ASYNC_PF_INT)) {
+        report_skip("KVM_FEATURE_ASYNC_PF_INT is not supported\n");
+        return report_summary();
+    }
        setup_vm();
-    printf("install handler\n");
-    handle_exception(14, pf_isr);
-    apf_reason = 0;
-    printf("enable async pf\n");
+
+    handle_exception(PF_VECTOR, handle_pf);
+    handle_irq(HYPERVISOR_CALLBACK_VECTOR, handle_interrupt);
+    memset(&apf_reason, 0, sizeof(apf_reason));
+
+    wrmsr(MSR_KVM_ASYNC_PF_INT, HYPERVISOR_CALLBACK_VECTOR);
      wrmsr(MSR_KVM_ASYNC_PF_EN, virt_to_phys((void*)&apf_reason) |
-            KVM_ASYNC_PF_SEND_ALWAYS | KVM_ASYNC_PF_ENABLED);
-    printf("alloc memory\n");
+            KVM_ASYNC_PF_SEND_ALWAYS | KVM_ASYNC_PF_ENABLED | KVM_ASYNC_PF_DELIVERY_AS_INT);
+
      buf = malloc(MEM);
      sti();
-    while(loop--) {
-        printf("start loop\n");
-        /* access a lot of memory to make host swap it out */
-        for (i=0; i < MEM; i+=4096)
-            buf[i] = 1;
-        printf("end loop\n");
-    }
-    cli();
  +    /* access a lot of memory to make host swap it out */
+    for (i = 0; i < MEM; i += 4096)
+        buf[i] = 1;
+
+    cli();
+    report(asyncpf_num > 0, "get %d async pf events ('page not present' #PF event with matched "
+        "'page ready' interrupt event )", asyncpf_num);
      return report_summary();
  }
diff --git a/x86/unittests.cfg b/x86/unittests.cfg
index 3fe59449..e3d051bc 100644
--- a/x86/unittests.cfg
+++ b/x86/unittests.cfg
@@ -172,7 +172,7 @@ extra_params = -cpu max
    [asyncpf]
  file = asyncpf.flat
-extra_params = -m 2048
+extra_params = -cpu host -m 2048
    [emulator]
  file = emulator.flat





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