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Re: [Qemu-devel] [PATCH v1] kvm: Make vcpu->requests as 64 bit bitmap
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From: |
Andrey Smetanin |
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Subject: |
Re: [Qemu-devel] [PATCH v1] kvm: Make vcpu->requests as 64 bit bitmap |
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Date: |
Thu, 24 Dec 2015 14:36:48 +0300 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 |
On 12/24/2015 02:14 PM, Roman Kagan wrote:
On Thu, Dec 24, 2015 at 12:30:26PM +0300, Andrey Smetanin wrote:
Currently on x86 arch we has already 32 requests defined
so the newer request bits can't be placed inside
vcpu->requests(unsigned long) inside x86 32 bit system.
But we are going to add a new request in x86 arch
for Hyper-V tsc page support.
To solve the problem the patch replaces vcpu->requests by
bitmap with 64 bit length and uses bitmap API.
The patch consists of:
* announce kvm_vcpu_has_requests() to check whether vcpu has
requests
* announce kvm_vcpu_requests() to get vcpu requests pointer
I think that if abstracting out the implementation of the request
container is what you're after, you'd better not define this function;
accesses to the request map should be through your accessor functions.
Good idea! I'll rework this patch and will send V2.
* announce kvm_clear_request() to clear particular vcpu request
* replace if (vcpu->requests) by if (kvm_vcpu_has_requests(vcpu))
* replace clear_bit(req, vcpu->requests) by
kvm_clear_request(req, vcpu)
Apparently one accessor is missing: test the presence of a request
without clearing it from the bitmap (because kvm_check_request() clears
it).
agree
diff --git a/arch/powerpc/kvm/trace.h b/arch/powerpc/kvm/trace.h
index 2e0e67e..4015b88 100644
--- a/arch/powerpc/kvm/trace.h
+++ b/arch/powerpc/kvm/trace.h
@@ -109,7 +109,7 @@ TRACE_EVENT(kvm_check_requests,
TP_fast_assign(
__entry->cpu_nr = vcpu->vcpu_id;
- __entry->requests = vcpu->requests;
+ __entry->requests = (__u32)kvm_vcpu_requests(vcpu)[0];
),
This doesn't make sense, to expose only subset of the requests. BTW I
don't see this event in Linus tree, nor in linux-next,
I found it here:
arch/powerpc/kvm/powerpc.c:104: trace_kvm_check_requests(vcpu);
>so I'm not quite
sure why it's formed this way; I guess the interesting part is the
request number and the return value (i.e. whether it's set), not the
whole bitmap.
No, the code actually dumps part of first 32 bit of bitmap:
TP_printk("vcpu=%x requests=%x",
__entry->cpu_nr, __entry->requests)
So, for this corner case we can make __entry->requests as unsigned long
variable and make the API helper to get first unsigned long from
vcpu->requests bitmap. Next print part of bitmap this way:
TP_printk("vcpu=0x%x requests=0x%lx",
__entry->cpu_nr, __entry->requests)
(as unsigned long).
POWERPC guys what do you think about such approach? Or could
we even drop trace_kvm_check_requests() at all. Does
trace_kvm_check_requests() still useful for you?
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5957,7 +5957,7 @@ static int handle_invalid_guest_state(struct kvm_vcpu
*vcpu)
if (intr_window_requested && vmx_interrupt_allowed(vcpu))
return handle_interrupt_window(&vmx->vcpu);
- if (test_bit(KVM_REQ_EVENT, &vcpu->requests))
+ if (test_bit(KVM_REQ_EVENT, kvm_vcpu_requests(vcpu)))
Here you'd rather want that function to test for the request without
clearing it.
agree, i'll provide such function.
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2117,7 +2117,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct
msr_data *msr_info)
if (ka->boot_vcpu_runs_old_kvmclock != tmp)
set_bit(KVM_REQ_MASTERCLOCK_UPDATE,
- &vcpu->requests);
+ kvm_vcpu_requests(vcpu));
This should have been kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
agree
@@ -8048,7 +8048,7 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu
*vcpu)
if (atomic_read(&vcpu->arch.nmi_queued))
return true;
- if (test_bit(KVM_REQ_SMI, &vcpu->requests))
+ if (test_bit(KVM_REQ_SMI, kvm_vcpu_requests(vcpu)))
Again the test-only accessor is due here.
agree
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -146,6 +146,8 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_HV_EXIT 30
#define KVM_REQ_HV_STIMER 31
+#define KVM_REQ_MAX 64
+
#define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
@@ -233,7 +235,7 @@ struct kvm_vcpu {
int vcpu_id;
int srcu_idx;
int mode;
- unsigned long requests;
+ DECLARE_BITMAP(requests, KVM_REQ_MAX);
unsigned long guest_debug;
int pre_pcpu;
@@ -286,6 +288,16 @@ struct kvm_vcpu {
struct kvm_vcpu_arch arch;
};
+static inline bool kvm_vcpu_has_requests(struct kvm_vcpu *vcpu)
+{
+ return !bitmap_empty(vcpu->requests, KVM_REQ_MAX);
+}
+
+static inline ulong *kvm_vcpu_requests(struct kvm_vcpu *vcpu)
+{
+ return (ulong *)vcpu->requests;
+}
As I wrote above, I believe this function doesn't belong in the API.
agree, i'll drop it.
+
static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
{
return cmpxchg(&vcpu->mode, IN_GUEST_MODE, EXITING_GUEST_MODE);
@@ -1002,7 +1014,7 @@ static inline bool kvm_is_error_gpa(struct kvm *kvm,
gpa_t gpa)
static inline void kvm_migrate_timers(struct kvm_vcpu *vcpu)
{
- set_bit(KVM_REQ_MIGRATE_TIMER, &vcpu->requests);
+ set_bit(KVM_REQ_MIGRATE_TIMER, kvm_vcpu_requests(vcpu));
kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu);
agree
@@ -1118,19 +1130,24 @@ static inline bool kvm_vcpu_compatible(struct kvm_vcpu
*vcpu) { return true; }
static inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
{
- set_bit(req, &vcpu->requests);
+ set_bit(req, kvm_vcpu_requests(vcpu));
}
static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
{
- if (test_bit(req, &vcpu->requests)) {
- clear_bit(req, &vcpu->requests);
+ if (test_bit(req, kvm_vcpu_requests(vcpu))) {
+ clear_bit(req, kvm_vcpu_requests(vcpu));
return true;
} else {
return false;
}
I wonder why this doesn't use test_and_clear_bit instead.
agree, i'll replace it by test_and_clear_bit
Roman.