[PATCH v2] spapr: Add "memop" hypercall

Benjamin Herrenschmidt
2012-05-25T03:53:27Z

This adds a qemu-specific hypervisor call to the pseries machine
which allows to do what amounts to memmove, memcpy and xor over
regions of physical memory such as the framebuffer.

This is the simplest way to get usable framebuffer speed from
SLOF since the framebuffer isn't mapped in the VRMA and so would
otherwise require an hcall per 8 bytes access.

The performance is still not great but usable, and can be improved
with a more complex implementation of the hcall itself if needed.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

v2: - Added documentation for our private hcalls
- Fixed coding style issues

docs/specs/ppc-spapr-hcalls.txt | 78 +++++++++++++++++++++++++++++++++++++++
hw/spapr.h | 3 +-
hw/spapr_hcall.c | 52 ++++++++++++++++++++++++++
3 files changed, 132 insertions(+), 1 deletions(-)
create mode 100644 docs/specs/ppc-spapr-hcalls.txt

diff --git a/docs/specs/ppc-spapr-hcalls.txt b/docs/specs/ppc-spapr-hcalls.txt
new file mode 100644
index 0000000..4b3fa9a
--- /dev/null
+++ b/docs/specs/ppc-spapr-hcalls.txt
@@ -0,0 +1,78 @@
+When used with the "pseries" machine type, qemu-system-ppc64 implement
+a set of hypervisor calls using a subset of the server "PAPR" specification
+(IBM internal at this point), which is also what IBM proprietary hypervisor
+adheres too.
+
+The subset is selected based on the requirements of Linux as a guest.
+
+In addition to those calls, we have added our own private hypervisor
+calls which are mostly used as a private interface between the firmware
+running in the guest and qemu.
+
+All those hypercalls start at hcall number 0xf000 which correspond
+to a implementation specific range in PAPR.
+
+- H_RTAS (0xf000)
+
+RTAS is a set of runtime services generally provided by the firmware
+inside the guest to the operating system. It predates the existence
+of hypervisors (it was originally an extension to Open Firmware) and
+is still used by PAPR to provide various services that aren't performance
+sensitive.
+
+We currently implement the RTAS services in qemu itself. The actual RTAS
+"firmware" blob in the guest is a small stub of a few instructions which
+calls our private H_RTAS hypervisor call to pass the RTAS calls to qemu.
+
+Arguments:
+
+ r3 : H_RTAS (0xf000)
+ r4 : Guest physical address of RTAS parameter block
+
+Returns:
+
+ H_SUCCESS : Successully called the RTAS function (RTAS result
+ will have been stored in the parameter block)
+ H_PARAMETER : Unknown token
+
+- H_LOGICAL_MEMOP (0xf001)
+
+When the guest runs in "real mode" (in powerpc lingua this means
+with MMU disabled, ie guest effective = guest physical), it only
+has access to a subset of memory and no IOs.
+
+PAPR provides a set of hypervisor calls to perform cachable or
+non-cachable accesses to any guest physical addresses that the
+guest can use in order to access IO devices while in real mode.
+
+This is typically used by the firmware running in the guest.
+
+However, doing a hypercall for each access is extremely inefficient
+(even more so when running KVM) when accessing the frame buffer. In
+that case, things like scrolling become unusably slow.
+
+This hypercall allows the guest to request a "memory op" to be applied
+to memory. The supported memory ops at this point are to copy a range
+of memory (supports overlap of source and destination) and XOR which
+is used by our SLOF firmware to invert the screen.
+
+Arguments:
+
+ r3: H_LOGICAL_MEMOP (0xf001)
+ r4: Guest physical address of destination
+ r5: Guest physical address of source
+ r6: Individual element size
+ 0 = 1 byte
+ 1 = 2 bytes
+ 2 = 4 bytes
+ 3 = 8 bytes
+ r7: Number of elements
+ r8: Operation
+ 0 = copy
+ 1 = xor
+
+Returns:
+
+ H_SUCCESS : Success
+ H_PARAMETER : Invalid argument
+
diff --git a/hw/spapr.h b/hw/spapr.h
index 7c497aa..0343f33 100644
--- a/hw/spapr.h
+++ b/hw/spapr.h
@@ -264,7 +264,8 @@ typedef struct sPAPREnvironment {
*/
#define KVMPPC_HCALL_BASE 0xf000
#define KVMPPC_H_RTAS (KVMPPC_HCALL_BASE + 0x0)
-#define KVMPPC_HCALL_MAX KVMPPC_H_RTAS
+#define KVMPPC_H_LOGICAL_MEMOP (KVMPPC_HCALL_BASE + 0x1)
+#define KVMPPC_HCALL_MAX KVMPPC_H_LOGICAL_MEMOP

extern sPAPREnvironment *spapr;

diff --git a/hw/spapr_hcall.c b/hw/spapr_hcall.c
index 94bb504..5211364 100644
--- a/hw/spapr_hcall.c
+++ b/hw/spapr_hcall.c
@@ -608,6 +608,57 @@ static target_ulong h_logical_store(CPUPPCState *env, sPAPREnvironment *spapr,
return H_PARAMETER;
}

+static target_ulong h_logical_memop(CPUPPCState *env, sPAPREnvironment *spapr,
+ target_ulong opcode, target_ulong *args)
+{
+ target_ulong dst = args[0]; /* Destination address */
+ target_ulong src = args[1]; /* Source address */
+ target_ulong esize = args[2]; /* Element size (0=1,1=2,2=4,3=8) */
+ target_ulong count = args[3]; /* Element count */
+ target_ulong op = args[4]; /* 0 = copy, 1 = invert */
+ uint64_t tmp;
+ unsigned int mask = (1 << esize) - 1;
+ int step = 1 << esize;
+
+ if (count > 0x80000000) {
+ return H_PARAMETER;
+ }
+
+ if ((dst & mask) || (src & mask)) {
+ return H_PARAMETER;
+ }
+
+ if (dst >= src && dst < (src + (count << esize))) {
+ dst = dst + ((count - 1) << esize);
+ src = src + ((count - 1) << esize);
+ step = -step;
+ }
+
+ while (count--) {
+ switch (esize) {
+ case 0: tmp = ldub_phys(src); break;
+ case 1: tmp = lduw_phys(src); break;
+ case 2: tmp = ldl_phys(src); break;
+ case 3: tmp = ldq_phys(src); break;
+ default:
+ return H_PARAMETER;
+ }
+ if (op) {
+ tmp = ~tmp;
+ }
+ switch (esize) {
+ case 0: stb_phys(dst, tmp); break;
+ case 1: stw_phys(dst, tmp); break;
+ case 2: stl_phys(dst, tmp); break;
+ case 3: stq_phys(dst, tmp); break;
+ }
+ dst = dst + step;
+ src = src + step;
+ }
+
+ return H_SUCCESS;
+}
+
static target_ulong h_logical_icbi(CPUPPCState *env, sPAPREnvironment *spapr,
target_ulong opcode, target_ulong *args)
{
@@ -700,6 +751,7 @@ static void hypercall_register_types(void)
spapr_register_hypercall(H_LOGICAL_CACHE_STORE, h_logical_store);
spapr_register_hypercall(H_LOGICAL_ICBI, h_logical_icbi);
spapr_register_hypercall(H_LOGICAL_DCBF, h_logical_dcbf);
+ spapr_register_hypercall(KVMPPC_H_LOGICAL_MEMOP, h_logical_memop);

/* qemu/KVM-PPC specific hcalls */
spapr_register_hypercall(KVMPPC_H_RTAS, h_rtas);