On Thu Jun 6, 2024 at 10:16 PM AEST, Aditya Gupta wrote:
> Power11 has the same PCR (Processor Compatibility Register) value, as
> Power10.
>
> Due to this, QEMU considers Power11 as a valid compat-mode for Power10,
> ie. earlier it was possible to run QEMU with '-M
> pseries,max-compat-mode=power11 --cpu power10'
Isn't this expected to work, or no?
>
> Same PCR also introduced a regression where `-M pseries --cpu power10`
> boots as Power11 (ie. logical PVR is of Power11, even though PVR is Power10).
> The regression was due to 'do_client_architecture_support' checking for
> valid compat modes and finding Power11 to be a valid compat mode for
> Power10 (it happens even without passing 'max-compat-mode' explicitly).
>
> Fix compat-mode issue and regression, by ensuring a future Power
> processor (with a higher logical_pvr value, eg. P11) cannot be valid
> compat-mode for an older Power processor (eg. P10)
This should be done before introducing the Power11 CPU so there's no
regression inside the series.
>
> Cc: Cédric Le Goater <c...@kaod.org>
> Cc: Daniel Henrique Barboza <danielhb...@gmail.com>
> Cc: Harsh Prateek Bora <hars...@linux.ibm.com>
> Cc: Mahesh J Salgaonkar <mah...@linux.ibm.com>
> Cc: Madhavan Srinivasan <ma...@linux.ibm.com>
> Cc: Nicholas Piggin <npig...@gmail.com>
> Signed-off-by: Aditya Gupta <adit...@linux.ibm.com>
> ---
> target/ppc/compat.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/target/ppc/compat.c b/target/ppc/compat.c
> index 12dd8ae290ca..168a3c06316f 100644
> --- a/target/ppc/compat.c
> +++ b/target/ppc/compat.c
> @@ -139,6 +139,10 @@ static bool pcc_compat(PowerPCCPUClass *pcc, uint32_t
> compat_pvr,
> /* Outside specified range */
> return false;
> }
> + if (compat->pvr > pcc->logical_pvr) {
> + /* Older CPU cannot support a newer processor's compat mode */
> + return false;
> + }
Hmm. I suppose this is the right way to fix it.
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> if (!(pcc->pcr_supported & compat->pcr_level)) {
> /* Not supported by this CPU */
> return false;
