RFC: simplify kvm-userspace to qemu-kvm callback structure

Background:
In our ppc code for the demo we only needed a call to cpu_physical_memory_rw to handle all kind of mmio we needed. Looking at all the callback pointers for read/write mmio in kvm_callbacks I wondered if this can be simplified with cpu_physical_memory_rw for x86 too. So I tested it today and it works fine on with kvm-svm on my opteron. The only code that did not just redirect to another function was a workaround for a Redhat 7.1 issue, so I merged it in the central call making it easier to find and maintain (was split before) anyway.
If everyone agrees with it I will create a new patch also affecting the other implementations of this interface e.g. user/main.c and a rebased version of this one.
But maybe there was a reason to do it that split way with all the callback pointers that was not obvious to me, so please comment.

P.S. up to now I did not find such a single function in qemu to handle the normal I/O (non mm), but maybe there is more potential to slimline that callback stuff.

---

Subject: [PATCH] simplify kvm-userspace to qemu-kvm callback structure

From: Christian Ehrhardt <[email protected]>

Merging the kvm callback elements write[bwlq] and read[bwlq] into a single call simplifying that interface.
Additionally this patch fixes a small typo and combines two workarounds for the same issue in code the patch touches anyway.

---

[diffstat]

libkvm/libkvm.c |   40 ++++--------------------------------
libkvm/libkvm.h |   19 ++---------------
qemu/qemu-kvm.c |   62 +++-----------------------------------------------------
3 files changed, 12 insertions(+), 109 deletions(-)

[diff (also attached)]

index 573a9ab..057706c 100644
@@ -771,44 +771,14 @@ static int handle_mmio(kvm_context_t kvm, struct kvm_run *kvm_run)

{
	unsigned long addr = kvm_run->mmio.phys_addr;
	void *data = kvm_run->mmio.data;

- int r = -1;

- /* hack: Red Hat 7.1 generates these wierd accesses. */
- if (addr == 0xa0000 && kvm_run->mmio.len == 3)
+ /* hack: Red Hat 7.1 generates these weird accesses. */
+ if ((addr > 0xa0000-4 && addr <= 0xa0000) && kvm_run->mmio.len == 3)

	    return 0;

- if (kvm_run->mmio.is_write) {
- switch (kvm_run->mmio.len) {
- case 1:
- r = kvm->callbacks->writeb(kvm->opaque, addr, *(uint8_t *)data);
- break;
- case 2:
- r = kvm->callbacks->writew(kvm->opaque, addr, *(uint16_t *)data);
- break;
- case 4:
- r = kvm->callbacks->writel(kvm->opaque, addr, *(uint32_t *)data);
- break;
- case 8:
- r = kvm->callbacks->writeq(kvm->opaque, addr, *(uint64_t *)data);
- break;
- }
- } else {
- switch (kvm_run->mmio.len) {
- case 1:
- r = kvm->callbacks->readb(kvm->opaque, addr, (uint8_t *)data);
- break;
- case 2:
- r = kvm->callbacks->readw(kvm->opaque, addr, (uint16_t *)data);
- break;
- case 4:
- r = kvm->callbacks->readl(kvm->opaque, addr, (uint32_t *)data);
- break;
- case 8:
- r = kvm->callbacks->readq(kvm->opaque, addr, (uint64_t *)data);
- break;
- }
- }
- return r;
+ return kvm->callbacks->mmio_rw(kvm->opaque, addr, data,
+ kvm_run->mmio.len,
+ kvm_run->mmio.is_write);
}

int handle_io_window(kvm_context_t kvm)

index ff260f4..d44a364 100644
@@ -45,22 +45,9 @@ struct kvm_callbacks {
    int (*outw)(void *opaque, uint16_t addr, uint16_t data);

	/// For 32bit IO writes from the guest (Usually when executing 'outl')
    int (*outl)(void *opaque, uint16_t addr, uint32_t data);

- /// For 8bit memory reads from unmapped memory (For MMIO devices)
- int (*readb)(void *opaque, uint64_t addr, uint8_t *data);
- /// For 16bit memory reads from unmapped memory (For MMIO devices)
- int (*readw)(void *opaque, uint64_t addr, uint16_t *data);
- /// For 32bit memory reads from unmapped memory (For MMIO devices)
- int (*readl)(void *opaque, uint64_t addr, uint32_t *data);
- /// For 64bit memory reads from unmapped memory (For MMIO devices)
- int (*readq)(void *opaque, uint64_t addr, uint64_t *data);
- /// For 8bit memory writes to unmapped memory (For MMIO devices)
- int (*writeb)(void *opaque, uint64_t addr, uint8_t data);
- /// For 16bit memory writes to unmapped memory (For MMIO devices)
- int (*writew)(void *opaque, uint64_t addr, uint16_t data);
- /// For 32bit memory writes to unmapped memory (For MMIO devices)
- int (*writel)(void *opaque, uint64_t addr, uint32_t data);
- /// For 64bit memory writes to unmapped memory (For MMIO devices)
- int (*writeq)(void *opaque, uint64_t addr, uint64_t data);
+ /// generic memory writes to unmapped memory (For MMIO devices)
+ int (*mmio_rw)(void *opaque, uint64_t addr, uint8_t *data,

+					int len, int is_write);
    int (*debug)(void *opaque, int vcpu);
	/*!
	 * \brief Called when the VCPU issues an 'hlt' instruction.

index 3aeba39..2b61a42 100644
@@ -477,58 +477,11 @@ static int kvm_outl(void *opaque, uint16_t addr, uint32_t data)
    return 0;

}

-static int kvm_readb(void *opaque, uint64_t addr, uint8_t *data) +static int kvm_mmio_rw(void *opaque, uint64_t addr,
+ uint8_t *data, int len, int is_write)
{
- *data = ldub_phys(addr);
- return 0;
-}
- -static int kvm_readw(void *opaque, uint64_t addr, uint16_t *data) -{
- *data = lduw_phys(addr);
- return 0;
-}
-
-static int kvm_readl(void *opaque, uint64_t addr, uint32_t *data) -{
- /* hack: Red Hat 7.1 generates some wierd accesses. */
- if (addr > 0xa0000 - 4 && addr < 0xa0000) {
- *data = 0;

+	cpu_physical_memory_rw(addr,data,len,is_write);
	return 0;

- }
-
- *data = ldl_phys(addr);
- return 0;
-}
-
-static int kvm_readq(void *opaque, uint64_t addr, uint64_t *data) -{
- *data = ldq_phys(addr);
- return 0;
-}
-
-static int kvm_writeb(void *opaque, uint64_t addr, uint8_t data) -{
- stb_phys(addr, data);
- return 0;
-}
-
-static int kvm_writew(void *opaque, uint64_t addr, uint16_t data) -{
- stw_phys(addr, data);
- return 0;
-}
-
-static int kvm_writel(void *opaque, uint64_t addr, uint32_t data) -{
- stl_phys(addr, data);
- return 0;
-}
-
-static int kvm_writeq(void *opaque, uint64_t addr, uint64_t data) -{
- stq_phys(addr, data);
- return 0;
}

static int kvm_io_window(void *opaque)
@@ -556,14 +509,7 @@ static struct kvm_callbacks qemu_kvm_ops = {

    .outb  = kvm_outb,
    .outw  = kvm_outw,
    .outl  = kvm_outl,
-    .readb = kvm_readb,
-    .readw = kvm_readw,
-    .readl = kvm_readl,
-    .readq = kvm_readq,
-    .writeb = kvm_writeb,
-    .writew = kvm_writew,
-    .writel = kvm_writel,
-    .writeq = kvm_writeq,
+    .mmio_rw = kvm_mmio_rw,

.halt = kvm_halt,
.shutdown = kvm_shutdown,
.io_window = kvm_io_window,

Grüsse / regards, Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
[email protected]
[email protected]

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen Geschäftsführung: Herbert Kircher Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294

index 573a9ab..057706c 100644
@@ -771,44 +771,14 @@ static int handle_mmio(kvm_context_t kvm, struct kvm_run *kvm_run)
 {
 	unsigned long addr = kvm_run->mmio.phys_addr;
 	void *data = kvm_run->mmio.data;
-	int r = -1;
 
-	/* hack: Red Hat 7.1 generates these wierd accesses. */
-	if (addr == 0xa0000 && kvm_run->mmio.len == 3)
+	/* hack: Red Hat 7.1 generates these weird accesses. */
+	if ((addr > 0xa0000-4 && addr <= 0xa0000) && kvm_run->mmio.len == 3)
 	    return 0;
 
-	if (kvm_run->mmio.is_write) {
-		switch (kvm_run->mmio.len) {
-		case 1:
-			r = kvm->callbacks->writeb(kvm->opaque, addr, *(uint8_t *)data);
-			break;
-		case 2:
-			r = kvm->callbacks->writew(kvm->opaque, addr, *(uint16_t *)data);
-			break;
-		case 4:
-			r = kvm->callbacks->writel(kvm->opaque, addr, *(uint32_t *)data);
-			break;
-		case 8:
-			r = kvm->callbacks->writeq(kvm->opaque, addr, *(uint64_t *)data);
-			break;
-		}
-	} else {
-		switch (kvm_run->mmio.len) {
-		case 1:
-			r = kvm->callbacks->readb(kvm->opaque, addr, (uint8_t *)data);
-			break;
-		case 2:
-			r = kvm->callbacks->readw(kvm->opaque, addr, (uint16_t *)data);
-			break;
-		case 4:
-			r = kvm->callbacks->readl(kvm->opaque, addr, (uint32_t *)data);
-			break;
-		case 8:
-			r = kvm->callbacks->readq(kvm->opaque, addr, (uint64_t *)data);
-			break;
-		}
-	}
-	return r;
+	return kvm->callbacks->mmio_rw(kvm->opaque, addr, data,
+					kvm_run->mmio.len,
+					kvm_run->mmio.is_write);
 }
 
 int handle_io_window(kvm_context_t kvm)

index ff260f4..d44a364 100644
@@ -45,22 +45,9 @@ struct kvm_callbacks {
     int (*outw)(void *opaque, uint16_t addr, uint16_t data);
 	/// For 32bit IO writes from the guest (Usually when executing 'outl')
     int (*outl)(void *opaque, uint16_t addr, uint32_t data);
-	/// For 8bit memory reads from unmapped memory (For MMIO devices)
-    int (*readb)(void *opaque, uint64_t addr, uint8_t *data);
-	/// For 16bit memory reads from unmapped memory (For MMIO devices)
-    int (*readw)(void *opaque, uint64_t addr, uint16_t *data);
-	/// For 32bit memory reads from unmapped memory (For MMIO devices)
-    int (*readl)(void *opaque, uint64_t addr, uint32_t *data);
-	/// For 64bit memory reads from unmapped memory (For MMIO devices)
-    int (*readq)(void *opaque, uint64_t addr, uint64_t *data);
-	/// For 8bit memory writes to unmapped memory (For MMIO devices)
-    int (*writeb)(void *opaque, uint64_t addr, uint8_t data);
-	/// For 16bit memory writes to unmapped memory (For MMIO devices)
-    int (*writew)(void *opaque, uint64_t addr, uint16_t data);
-	/// For 32bit memory writes to unmapped memory (For MMIO devices)
-    int (*writel)(void *opaque, uint64_t addr, uint32_t data);
-	/// For 64bit memory writes to unmapped memory (For MMIO devices)
-    int (*writeq)(void *opaque, uint64_t addr, uint64_t data);
+	/// generic memory writes to unmapped memory (For MMIO devices)
+    int (*mmio_rw)(void *opaque, uint64_t addr, uint8_t *data,
+					int len, int is_write);
     int (*debug)(void *opaque, int vcpu);
 	/*!
 	 * \brief Called when the VCPU issues an 'hlt' instruction.

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It may be worthwhile to unify all the reads into a single read, but read and write are fundamentally different. The fact that qemu implements it in one function is a detail; libkvm aims to satisfy more than just qemu.

error compiling committee.c: too many arguments to function


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That's fair - I thought too qemu-centric while the interface should be generic.
I changed the simplification patch to have separate read/write calls, but not one per len. That still reduce the different callbacks for mmio from eight to two pointers.
To have it clean I put the updated patch in a separate mail.

P.S. Sorry for overlooking your response and asking again.

Grüsse / regards, 
Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
[email protected]
[email protected]

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen 
Geschäftsführung: Herbert Kircher 
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294

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Well no response might mean that there is nothing to be said against this simplification ;-)
Because of that I completed the patch (main.c as well) and corrected some whitespace issues I had before.

Grüsse / regards, 
Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
[email protected]
[email protected]

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen 
Geschäftsführung: Herbert Kircher 
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294

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I did respond, see
http://article.gmane.org/gmane.comp.emulators.kvm.devel/10467.

Any sufficiently difficult bug is indistinguishable from a feature.


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Subject: [PATCH] simplify read[bwlq]/write[bwlq] callback structure

From: Christian Ehrhardt <[email protected]>

Merging the read[bwlq]/write[bwlq] callback callback pointers to one mmio_rw function simplifies the callback interface (a lot of lines in libkvm.c and main.c) and eventually uses the qemu copy frontend
function cpu_physical_memory_rw.

---

[diffstat]

libkvm/libkvm.c |   40 ++++--------------------------------
libkvm/libkvm.h |   19 ++---------------
qemu/qemu-kvm.c |   62 +++-----------------------------------------------------
user/main.c     |   52 ++++++----------------------------------------
4 files changed, 19 insertions(+), 154 deletions(-)

[diff]
*Attached*

Grüsse / regards, Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
[email protected]
[email protected]

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen Geschäftsführung: Herbert Kircher Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294

index 573a9ab..057706c 100644
@@ -771,44 +771,14 @@ static int handle_mmio(kvm_context_t kvm, struct kvm_run *kvm_run)
 {
 	unsigned long addr = kvm_run->mmio.phys_addr;
 	void *data = kvm_run->mmio.data;
-	int r = -1;
 
-	/* hack: Red Hat 7.1 generates these wierd accesses. */
-	if (addr == 0xa0000 && kvm_run->mmio.len == 3)
+	/* hack: Red Hat 7.1 generates these weird accesses. */
+	if ((addr > 0xa0000-4 && addr <= 0xa0000) && kvm_run->mmio.len == 3)
 	    return 0;
 
-	if (kvm_run->mmio.is_write) {
-		switch (kvm_run->mmio.len) {
-		case 1:
-			r = kvm->callbacks->writeb(kvm->opaque, addr, *(uint8_t *)data);
-			break;
-		case 2:
-			r = kvm->callbacks->writew(kvm->opaque, addr, *(uint16_t *)data);
-			break;
-		case 4:
-			r = kvm->callbacks->writel(kvm->opaque, addr, *(uint32_t *)data);
-			break;
-		case 8:
-			r = kvm->callbacks->writeq(kvm->opaque, addr, *(uint64_t *)data);
-			break;
-		}
-	} else {
-		switch (kvm_run->mmio.len) {
-		case 1:
-			r = kvm->callbacks->readb(kvm->opaque, addr, (uint8_t *)data);
-			break;
-		case 2:
-			r = kvm->callbacks->readw(kvm->opaque, addr, (uint16_t *)data);
-			break;
-		case 4:
-			r = kvm->callbacks->readl(kvm->opaque, addr, (uint32_t *)data);
-			break;
-		case 8:
-			r = kvm->callbacks->readq(kvm->opaque, addr, (uint64_t *)data);
-			break;
-		}
-	}
-	return r;
+	return kvm->callbacks->mmio_rw(kvm->opaque, addr, data,
+					kvm_run->mmio.len,
+					kvm_run->mmio.is_write);
 }
 
 int handle_io_window(kvm_context_t kvm)

index ff260f4..d44a364 100644
@@ -45,22 +45,9 @@ struct kvm_callbacks {
     int (*outw)(void *opaque, uint16_t addr, uint16_t data);
 	/// For 32bit IO writes from the guest (Usually when executing 'outl')
     int (*outl)(void *opaque, uint16_t addr, uint32_t data);
-	/// For 8bit memory reads from unmapped memory (For MMIO devices)
-    int (*readb)(void *opaque, uint64_t addr, uint8_t *data);
-	/// For 16bit memory reads from unmapped memory (For MMIO devices)
-    int (*readw)(void *opaque, uint64_t addr, uint16_t *data);
-	/// For 32bit memory reads from unmapped memory (For MMIO devices)
-    int (*readl)(void *opaque, uint64_t addr, uint32_t *data);
-	/// For 64bit memory reads from unmapped memory (For MMIO devices)
-    int (*readq)(void *opaque, uint64_t addr, uint64_t *data);
-	/// For 8bit memory writes to unmapped memory (For MMIO devices)
-    int (*writeb)(void *opaque, uint64_t addr, uint8_t data);
-	/// For 16bit memory writes to unmapped memory (For MMIO devices)
-    int (*writew)(void *opaque, uint64_t addr, uint16_t data);
-	/// For 32bit memory writes to unmapped memory (For MMIO devices)
-    int (*writel)(void *opaque, uint64_t addr, uint32_t data);
-	/// For 64bit memory writes to unmapped memory (For MMIO devices)
-    int (*writeq)(void *opaque, uint64_t addr, uint64_t data);
+	/// generic memory writes to unmapped memory (For MMIO devices)
+    int (*mmio_rw)(void *opaque, uint64_t addr, uint8_t *data,
+					int len, int is_write);
     int (*debug)(void *opaque, int vcpu);
 	/*!
 	 * \brief Called when the VCPU issues an 'hlt' instruction.

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