On Mon Mar 3, 2025 at 8:58 PM AEST, BALATON Zoltan wrote:
> On Mon, 3 Mar 2025, Nicholas Piggin wrote:
>> Perform !guest_visible memory accesses without modifying R/C bits.
>>
>> It's arguable whether !guest_visible memory accesses should modify
>> R/C bits. i386 seems to set accessed/dirty bit updates for "probe"
>> accesses, but ppc with radix MMU does not. Follow the ppc/radix
>> lead and perform the accesses without updating R/C bits.
>>
>> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
>> ---
>> target/ppc/mmu-hash32.c | 27 ++++++++++++++-------------
>> target/ppc/mmu-hash64.c | 27 ++++++++++++++-------------
>> 2 files changed, 28 insertions(+), 26 deletions(-)
>>
>> diff --git a/target/ppc/mmu-hash32.c b/target/ppc/mmu-hash32.c
>> index 1f791a7f2f7..b8d7f87507b 100644
>> --- a/target/ppc/mmu-hash32.c
>> +++ b/target/ppc/mmu-hash32.c
>> @@ -410,19 +410,20 @@ bool ppc_hash32_xlate(PowerPCCPU *cpu, vaddr eaddr,
>> MMUAccessType access_type,
>> qemu_log_mask(CPU_LOG_MMU, "PTE access granted !\n");
>>
>> /* 8. Update PTE referenced and changed bits if necessary */
>> -
>> - if (!(pte.pte1 & HPTE32_R_R)) {
>> - ppc_hash32_set_r(cpu, pte_offset, pte.pte1);
>> - }
>> - if (!(pte.pte1 & HPTE32_R_C)) {
>> - if (access_type == MMU_DATA_STORE) {
>> - ppc_hash32_set_c(cpu, pte_offset, pte.pte1);
>> - } else {
>> - /*
>> - * Treat the page as read-only for now, so that a later write
>> - * will pass through this function again to set the C bit
>> - */
>> - prot &= ~PAGE_WRITE;
>> + if (guest_visible) {
>
> Are these unlikely() ? Not sure if that makes a difference but if we know
> it may help some compilers.
Yes it probably is. Although we don't tend to use unlikely very much. I
guess we have to start somewhere.
Thanks,
Nick
