Re: [PATCH 18/26] KVM: PPC: KVM PV guest stubs

On 06/27/2010 12:47 PM, Alexander Graf wrote:

Am 27.06.2010 um 10:28 schrieb Avi Kivity [off-list ref]:

quoted

On 06/26/2010 02:25 AM, Alexander Graf wrote:

quoted

We will soon start and replace instructions from the text section with
other, paravirtualized versions. To ease the readability of those 
patches
I split out the generic looping and magic page mapping code out.

This patch still only contains stubs. But at least it loops through the
text section :).


+
+static void kvm_check_ins(u32 *inst)
+{
+    u32 _inst = *inst;
+    u32 inst_no_rt = _inst&  ~KVM_MASK_RT;
+    u32 inst_rt = _inst&  KVM_MASK_RT;
+
+    switch (inst_no_rt) {
+    }
+
+    switch (_inst) {
+    }
+
+    flush_icache_range((ulong)inst, (ulong)inst + 4);
+}

Shouldn't we flush only if we patched something?

We introduce the patching in the next patches. This is only a 
preparation stub.

Well, unless I missed something, this remains unconditional after all 
the patches.

A helper patch(pc, replacement) could patch and flush in one go.

quoted

quoted

+
+static void kvm_use_magic_page(void)
+{
+    u32 *p;
+    u32 *start, *end;
+
+    /* Tell the host to map the magic page to -4096 on all CPUs */
+
+    on_each_cpu(kvm_map_magic_page, NULL, 1);
+
+    /* Now loop through all code and find instructions */
+
+    start = (void*)_stext;
+    end = (void*)_etext;
+
+    for (p = start; p<  end; p++)
+        kvm_check_ins(p);
+}
+

Or, flush the entire thing here.

I did that at first. It breaks. During the patching we may take 
interrupts (pahe faults for example) that contain just patched 
instructions. And really, hell breaks loose if we don't flush it 
immediately :). I was hoping at first a 32 bit replace would be atomic 
in cache, but the cpu tried to execute invalid instructions, so it 
must have gotten some intermediate state.

Surprising.  Maybe you need a flush after writing to the out-of-line code?

-- 
error compiling committee.c: too many arguments to function