Re: [PATCH v2 2/2] RISC-V: Consolidate isa correctness check

[Atish Patra <Atish.Patra@wdc.com>]

On Fri, 2019-10-18 at 01:43 -0700, Paul Walmsley wrote:
> On Wed, 9 Oct 2019, Atish Patra wrote:
> 
> > Currently, isa string is read and checked for correctness at
> > multiple
> > places.
> > 
> > Consolidate them into one function and use it only during early
> > bootup.
> > In case of a incorrect isa string, the cpu shouldn't boot at all.
> > 
> > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> 
> Looks like riscv_read_check_isa() is called twice for each hart.  Is
> there 
> any way to call it only once per hart?
> 

I had to add the check in riscv_fill_hwcap() because that function is
iterating over all cpu nodes to set the hwcap. Thus, some of the harts
that are not available due to incorrect isa string can affect hwcap.

We can check cpu_possible_mask to figure out the harts with invalid isa
strings but that will perform poorly as RISC-V have more harts in
future.


> 
> - Paul
> 
> > ---
> >  arch/riscv/include/asm/processor.h |  1 +
> >  arch/riscv/kernel/cpu.c            | 41 ++++++++++++++++++++++--
> > ------
> >  arch/riscv/kernel/cpufeature.c     |  4 +--
> >  arch/riscv/kernel/smpboot.c        |  4 +++
> >  4 files changed, 37 insertions(+), 13 deletions(-)
> > 
> > diff --git a/arch/riscv/include/asm/processor.h
> > b/arch/riscv/include/asm/processor.h
> > index f539149d04c2..189bf98f9a3f 100644
> > --- a/arch/riscv/include/asm/processor.h
> > +++ b/arch/riscv/include/asm/processor.h
> > @@ -74,6 +74,7 @@ static inline void wait_for_interrupt(void)
> >  }
> >  
> >  struct device_node;
> > +int riscv_read_check_isa(struct device_node *node, const char
> > **isa);
> >  int riscv_of_processor_hartid(struct device_node *node);
> >  
> >  extern void riscv_fill_hwcap(void);
> > diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> > index 40a3c442ac5f..6bd4c7176bf6 100644
> > --- a/arch/riscv/kernel/cpu.c
> > +++ b/arch/riscv/kernel/cpu.c
> > @@ -8,13 +8,43 @@
> >  #include <linux/of.h>
> >  #include <asm/smp.h>
> >  
> > +int riscv_read_check_isa(struct device_node *node, const char
> > **isa)
> > +{
> > +	u32 hart;
> > +
> > +	if (of_property_read_u32(node, "reg", &hart)) {
> > +		pr_warn("Found CPU without hart ID\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	if (of_property_read_string(node, "riscv,isa", isa)) {
> > +		pr_warn("CPU with hartid=%d has no \"riscv,isa\"
> > property\n",
> > +			hart);
> > +		return -ENODEV;
> > +	}
> > +	/*
> > +	 * Linux doesn't support rv32e or rv128i, and we only support
> > booting
> > +	 * kernels on harts with the same ISA that the kernel is
> > compiled for.
> > +	 */
> > +	if (IS_ENABLED(CONFIG_32BIT) && (strncmp(*isa, "rv32i", 5) !=
> > 0)) {
> > +		pr_warn("hartid=%d has an invalid ISA \"%s\" for 32bit
> > config\n",
> > +			hart, *isa);
> > +		return -ENODEV;
> > +	} else if (IS_ENABLED(CONFIG_64BIT) &&
> > +		  (strncmp(*isa, "rv64i", 5) != 0)) {
> > +		pr_warn("hartid=%d has an invalid ISA \"%s\" for 64bit
> > config\n",
> > +			hart, *isa);
> > +		return -ENODEV;
> > +	}
> > +	return 0;
> > +}
> > +
> >  /*
> >   * Returns the hart ID of the given device tree node, or -ENODEV
> > if the node
> >   * isn't an enabled and valid RISC-V hart node.
> >   */
> >  int riscv_of_processor_hartid(struct device_node *node)
> >  {
> > -	const char *isa;
> >  	u32 hart;
> >  
> >  	if (!of_device_is_compatible(node, "riscv")) {
> > @@ -32,15 +62,6 @@ int riscv_of_processor_hartid(struct device_node
> > *node)
> >  		return -ENODEV;
> >  	}
> >  
> > -	if (of_property_read_string(node, "riscv,isa", &isa)) {
> > -		pr_warn("CPU with hartid=%d has no \"riscv,isa\"
> > property\n", hart);
> > -		return -ENODEV;
> > -	}
> > -	if (isa[0] != 'r' || isa[1] != 'v') {
> > -		pr_warn("CPU with hartid=%d has an invalid ISA of
> > \"%s\"\n", hart, isa);
> > -		return -ENODEV;
> > -	}
> > -
> >  	return hart;
> >  }
> >  
> > diff --git a/arch/riscv/kernel/cpufeature.c
> > b/arch/riscv/kernel/cpufeature.c
> > index b1ade9a49347..eaad5aa07403 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -38,10 +38,8 @@ void riscv_fill_hwcap(void)
> >  		if (riscv_of_processor_hartid(node) < 0)
> >  			continue;
> >  
> > -		if (of_property_read_string(node, "riscv,isa", &isa)) {
> > -			pr_warn("Unable to find \"riscv,isa\"
> > devicetree entry\n");
> > +		if (riscv_read_check_isa(node, &isa) < 0)
> >  			continue;
> > -		}
> >  
> >  		for (i = 0; i < strlen(isa); ++i)
> >  			this_hwcap |= isa2hwcap[(unsigned
> > char)(isa[i])];
> > diff --git a/arch/riscv/kernel/smpboot.c
> > b/arch/riscv/kernel/smpboot.c
> > index 18ae6da5115e..15ee71297abf 100644
> > --- a/arch/riscv/kernel/smpboot.c
> > +++ b/arch/riscv/kernel/smpboot.c
> > @@ -60,12 +60,16 @@ void __init setup_smp(void)
> >  	int hart;
> >  	bool found_boot_cpu = false;
> >  	int cpuid = 1;
> > +	const char *isa;
> >  
> >  	for_each_of_cpu_node(dn) {
> >  		hart = riscv_of_processor_hartid(dn);
> >  		if (hart < 0)
> >  			continue;
> >  
> > +		if (riscv_read_check_isa(dn, &isa) < 0)
> > +			continue;
> > +
> >  		if (hart == cpuid_to_hartid_map(0)) {
> >  			BUG_ON(found_boot_cpu);
> >  			found_boot_cpu = 1;
> > -- 
> > 2.21.0
> > 
> > 
> 
> - Paul
> 
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-- 
Regards,
Atish
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