Re: [PATCH v2 1/4] powerpc/pseries: Limit PVR list to 16 entries for CAS negotiation
From: Amit Machhiwal <hidden>
Date: 2026-08-03 18:31:41
On 2026/08/03 09:27 PM, Mahesh Salgaonkar wrote:
quoted hunk ↗ jump to hunk
Current Power system firmware caps the PVR list array size at 16 entries during CAS (Client Architecture Support) negotiation. Passing more than capped size to older firmware could cause an undefined behaviour and breaks compatibility. Future Power system firmware releases will lift this restriction and support greater than 16 array entries. Ensure that when running on Power11 or below hardware, the number of PVR entries passed during CAS negotiation does not exceed the firmware-imposed limit of 16. In prom_send_capabilities(), compute start_index to skip the oldest leading pvrs[] entries when running on Power11 or below hardware, so that the pointer passed to ibm,client-architecture-support points to ibm_architecture_vec.pvrs[start_index], presenting exactly 16 entries to firmware. Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com> Tested-by: Praveen K Pandey <redacted> --- Change in v2: - Define a named macro CAS_MAX_PVR_ENTRIES --- arch/powerpc/kernel/prom_init.c | 35 ++++++++++++++++++++++++++------- 1 file changed, 28 insertions(+), 7 deletions(-)diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c index 53503937de0ee..6b50870759fd9 100644 --- a/arch/powerpc/kernel/prom_init.c +++ b/arch/powerpc/kernel/prom_init.c@@ -86,6 +86,12 @@ */ #define ADDR(x) (u32)(unsigned long)(x) +/* + * Current Power system firmware caps the PVR list array size at 16 entries + * during CAS (Client Architecture Support) negotiation. + */ +#define CAS_MAX_PVR_ENTRIES 16 + #ifdef CONFIG_PPC64 #define OF_WORKAROUNDS 0 #else@@ -979,6 +985,10 @@ static const struct ibm_arch_vec ibm_architecture_vec_template __initconst = { .mask = cpu_to_be32(0xfffe0000), /* POWER5/POWER5+ */ .val = cpu_to_be32(0x003a0000), }, + { + .mask = cpu_to_be32(0xffffffff), /* all 2.04-compliant and earlier */ + .val = cpu_to_be32(0x0f000001), + },
It may be a good idea to add a comment (like below) above .pvrs = {
explaining why the oldest entries are at the front, otherwise the intent
of start_index trimming from the front is not obvious to future
contributors:
/*
* The oldest/least-capable entries are placed at the FRONT so that
* start_index trims them first when running on older firmware (Power11
* and below) that caps the array at CAS_MAX_PVR_ENTRIES entries. As
* newer processors are added, more old front entries will naturally
* fall outside the firmware window. New entries must be inserted in
* newest-first order AFTER these oldest front entries.
*/
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{ .mask = cpu_to_be32(0xffff0000), /* POWER6 */ .val = cpu_to_be32(0x003e0000),@@ -1032,13 +1042,9 @@ static const struct ibm_arch_vec ibm_architecture_vec_template __initconst = { .val = cpu_to_be32(0x0f000003), }, { - .mask = cpu_to_be32(0xffffffff), /* all 2.05-compliant */ + .mask = cpu_to_be32(0xfffffffd), /* all 2.05-compliant */ .val = cpu_to_be32(0x0f000002), }, - { - .mask = cpu_to_be32(0xfffffffe), /* all 2.04-compliant and earlier */ - .val = cpu_to_be32(0x0f000001), - }, }, .num_vectors = NUM_VECTORS(6),@@ -1347,7 +1353,6 @@ static void __init prom_check_platform_support(void) }; int prop_len = prom_getproplen(prom.chosen, "ibm,arch-vec-5-platform-support"); -
Nit: Looks unintentional whitespace change, please drop.
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/* * First copy the architecture vec template *@@ -1403,6 +1408,22 @@ static void __init prom_send_capabilities(void) ihandle root; prom_arg_t ret; u32 cores; + int start_index = 0; + + /* + * Ensure that when running on Power11 or below hardware, the number + * of PVR entries passed during CAS negotiation does not exceed the + * firmware-imposed limit of 16. + * + * Compute the start_index to skip the oldest leading pvrs[] entries + * when running on Power11 or below hardware, so that the pointer + * passed to ibm,client-architecture-support points to + * ibm_architecture_vec.pvrs[start_index], presenting exactly 16 + * entries to firmware. + */ + if ((ARRAY_SIZE(ibm_architecture_vec_template.pvrs) > CAS_MAX_PVR_ENTRIES) && + (PVR_VER(mfspr(SPRN_PVR)) <= PVR_POWER11)) + start_index = ARRAY_SIZE(ibm_architecture_vec_template.pvrs) - CAS_MAX_PVR_ENTRIES; /* Check ibm,arch-vec-5-platform-support and fixup vec5 if required */ prom_check_platform_support();@@ -1427,7 +1448,7 @@ static void __init prom_send_capabilities(void) if (call_prom_ret("call-method", 3, 2, &ret, ADDR("ibm,client-architecture-support"), root, - ADDR(&ibm_architecture_vec)) == 0) { + ADDR(&ibm_architecture_vec.pvrs[start_index])) == 0) { /* the call exists... */ if (ret) prom_printf("\nWARNING: ibm,client-architecture"-- 2.55.0