On 6/2/21 12:18 PM, Bruno Larsen (billionai) wrote:

Based-on: <20210518201146.794854-1-richard.henderson@linaro.org>

This commit attempts to implement a first draft of a solution to the
first bug mentioned by Richard Henderson in this e-mail
https://lists.nongnu.org/archive/html/qemu-devel/2021-05/msg06247.html
The second bug was not touched, which is basically implementing the
solution C

To sumarize the first bug here, from my understanding, when an address
translation is asked of a 64bit mmu that uses hashtables, the code
attempts to check some permission bits, but checks them from the wrong
location.

The solution implemented here is more complex than necessary on
purpose, to make it more readable (and make sure I understand what is
going on). If that would really fix the problem, I'll move to
implementing an actual solution, and to all affected functions.

Signed-off-by: Bruno Larsen (billionai) <bruno.larsen@eldorado.org.br>
---
  target/ppc/mmu-hash64.c | 12 ++++++++++--
  1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/target/ppc/mmu-hash64.c b/target/ppc/mmu-hash64.c
index c1b98a97e9..63f10f1be7 100644
--- a/target/ppc/mmu-hash64.c
+++ b/target/ppc/mmu-hash64.c
@@ -887,6 +887,14 @@ bool ppc_hash64_xlate(PowerPCCPU *cpu, vaddr eaddr, MMUAccessType access_type,
      int exec_prot, pp_prot, amr_prot, prot;
      int need_prot;
      hwaddr raddr;
+    unsigned immu_idx, dmmu_idx;
+    immu_idx = (env->hflags >> HFLAGS_IMMU_IDX) & 7;
+    dmmu_idx = (env->hflags >> HFLAGS_DMMU_IDX) & 7;

This doesn't help at all with the reported bug. You're still reading from env. You need the mmu_idx that was passed to ppc_cpu_tlb_fill.

For the use from ppc_cpu_get_phys_page_debug, you'd pass in cpu_mmu_index(env, false).

ppc_cpu_get_phys_page_debug has 2 calls to ppc_xlate, one using the data MMU, the other using the instruction MMU. I'm guessing I should pass both, right?

But here we have another bit that confuses me: cpu_mmu_index returns 0 if in user mode, or uses the information stored in env to get it, so I don't see how that would be different from getting directly. Unless the point is to have ppc_*_xlate be generic and pc_*_debug knows the info in env is correct. Is that it?

+    const short HV = 1, IR = 2, DR = 3;
+    bool MSR[3];
+    MSR[HV] = dmmu_idx & 2,
+    MSR[IR] = immu_idx & 4,
+    MSR[DR] = dmmu_idx & 4;

There's no point in the array.  Just use three different scalars (real_mode, hv, and pr (note that pr is the major portion of the bug as reported)). Additionally, you'll not be distinguishing immu_idx and dmmu_idx, but using the single idx that's given.

Ah, yeah, that's the "more complex than necessary, but it was easy for me to read" part. Scalars are a good solution. In this function in specific, PR doesn't actually show up anywhere, so I would actually only need 2. Anyway, will start working on this.

-    if (access_type == MMU_INST_FETCH ? !msr_ir : !msr_dr) {
+    if (access_type == MMU_INST_FETCH ? !MSR[IR] : !MSR[DR]) {

Which simplifies this condition to just a single test.


r~