linux-kernel - Re: [PATCH] powerpc/bpf: Always reallocate BPF_REG_5, BPF_REG_AX and TMP

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Date:   Fri, 14 Jan 2022 08:03:47 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] powerpc/bpf: Always reallocate BPF_REG_5, BPF_REG_AX and
 TMP_REG when possible



Le 14/01/2022 à 08:58, Naveen N. Rao a écrit :
> Christophe Leroy wrote:
>> BPF_REG_5, BPF_REG_AX and TMP_REG are mapped on non volatile registers
>> because there are not enough volatile registers, but they don't need
>> to be preserved on function calls.
>>
>> So when some volatile registers become available, those registers can
>> always be reallocated regardless of whether SEEN_FUNC is set or not.
>>
>> Suggested-by: Naveen N. Rao <naveen.n.rao@...ux.ibm.com>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>  arch/powerpc/net/bpf_jit.h        |  3 ---
>>  arch/powerpc/net/bpf_jit_comp32.c | 14 +++++++++++---
>>  2 files changed, 11 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
>> index b20a2a83a6e7..b75507fc8f6b 100644
>> --- a/arch/powerpc/net/bpf_jit.h
>> +++ b/arch/powerpc/net/bpf_jit.h
>> @@ -127,9 +127,6 @@
>>  #define SEEN_FUNC    0x20000000 /* might call external helpers */
>>  #define SEEN_TAILCALL    0x40000000 /* uses tail calls */
>>
>> -#define SEEN_VREG_MASK    0x1ff80000 /* Volatile registers r3-r12 */
>> -#define SEEN_NVREG_MASK    0x0003ffff /* Non volatile registers 
>> r14-r31 */
>> -
>>  #ifdef CONFIG_PPC64
>>  extern const int b2p[MAX_BPF_JIT_REG + 2];
>>  #else
>> diff --git a/arch/powerpc/net/bpf_jit_comp32.c 
>> b/arch/powerpc/net/bpf_jit_comp32.c
>> index d3a52cd42f53..cfec42c8a511 100644
>> --- a/arch/powerpc/net/bpf_jit_comp32.c
>> +++ b/arch/powerpc/net/bpf_jit_comp32.c
>> @@ -77,14 +77,22 @@ static int bpf_jit_stack_offsetof(struct 
>> codegen_context *ctx, int reg)
>>      return BPF_PPC_STACKFRAME(ctx) - 4;
>>  }
>>
>> +#define SEEN_VREG_MASK        0x1ff80000 /* Volatile registers r3-r12 */
>> +#define SEEN_NVREG_FULL_MASK    0x0003ffff /* Non volatile registers 
>> r14-r31 */
>> +#define SEEN_NVREG_TEMP_MASK    0x00001e01 /* BPF_REG_5, BPF_REG_AX, 
>> TMP_REG */
> 
> Could have been named better: SEEN_NVREG_BPF_VGER_MASK, or such.

Yes, I was suffering from a lack of inspiration.

What does BPF_VGER mean ?


> Apart from that:
> Reviewed-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> 

Thanks