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List:       android-virt
Subject:    Re: [kvm-unit-tests PATCH 3/3] arm64: Add cache code generation test
From:       Andrew Jones <drjones () redhat ! com>
Date:       2019-09-30 15:10:10
Message-ID: 20190930151010.bizhegm3oh2cgefk () kamzik ! brq ! redhat ! com
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On Mon, Sep 30, 2019 at 03:25:08PM +0100, Alexandru Elisei wrote:
> Caches are a misterious creature on arm64, requiring a more hands-on
> approach from the programmer than on x86. When generating code, two cache
> maintenance operations are generally required: an invalidation for the
> stale instruction and a clean to the PoU (Point of Unification) for the new
> instruction. Fortunately, the ARM architecture has features to alleviate
> some of this overhead, which are advertised via the IDC and DIC bits in
> CTR_EL0: if IDC is 1, then the dcache clean is not required, and if DIC is
> 1, the icache invalidation can be absent. KVM exposes these bits to the
> guest.
> 
> Until Linux v4.16.1, KVM performed an icache invalidation each time a stage
> 2 page was mapped. This was then optimized so that the icache invalidation
> was performed when the guest tried to execute code from the page for the
> first time. And that was optimized again when support for the DIC bit was
> added to KVM.
> 
> The interactions between a guest that is generating code, the stage 2
> tables and the IDC and DIC bits can be subtle, especially when KVM
> optimizations come into play. Let's add a test that generates a few
> instructions and checks that KVM indeed honors those bits.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
>  arm/Makefile.arm64 |   1 +
>  arm/cache.c        | 122 +++++++++++++++++++++++++++++++++++++++++++++
>  arm/unittests.cfg  |   6 +++
>  3 files changed, 129 insertions(+)
>  create mode 100644 arm/cache.c
> 
> diff --git a/arm/Makefile.arm64 b/arm/Makefile.arm64
> index 35de5ea333b4..6d3dc2c4a464 100644
> --- a/arm/Makefile.arm64
> +++ b/arm/Makefile.arm64
> @@ -25,6 +25,7 @@ OBJDIRS += lib/arm64
>  # arm64 specific tests
>  tests = $(TEST_DIR)/timer.flat
>  tests += $(TEST_DIR)/micro-bench.flat
> +tests += $(TEST_DIR)/cache.flat
>  
>  include $(SRCDIR)/$(TEST_DIR)/Makefile.common
>  
> diff --git a/arm/cache.c b/arm/cache.c
> new file mode 100644
> index 000000000000..2939b85a8c9a
> --- /dev/null
> +++ b/arm/cache.c
> @@ -0,0 +1,122 @@
> +#include <libcflat.h>
> +#include <alloc_page.h>
> +#include <asm/mmu.h>
> +#include <asm/processor.h>
> +
> +#define NTIMES			(1 << 16)
> +
> +#define CTR_DIC			(1UL << 29)
> +#define CTR_IDC			(1UL << 28)
> +
> +#define CLIDR_LOC_SHIFT		24
> +#define CLIDR_LOC_MASK		(7UL << CLIDR_LOC_SHIFT)
> +#define CLIDR_LOUU_SHIFT	27
> +#define CLIDR_LOUU_MASK		(7UL << CLIDR_LOUU_SHIFT)
> +#define CLIDR_LOUIS_SHIFT	21
> +#define CLIDR_LOUIS_MASK	(7UL << CLIDR_LOUIS_SHIFT)
> +
> +#define RET			0xd65f03c0
> +#define MOV_X0(x)		(0xd2800000 | (((x) & 0xffff) << 5))
> +
> +#define clean_dcache_pou(addr)			\
> +	asm volatile("dc cvau, %0\n" :: "r" (addr) : "memory")
> +#define inval_icache_pou(addr)			\
> +	asm volatile("ic ivau, %0\n" :: "r" (addr) : "memory")
> +
> +typedef int (*fn_t)(void);
> +
> +static inline void prime_icache(u32 *code, u32 insn)
> +{
> +	*code = insn;
> +	/* This is the sequence recommended in ARM DDI 0487E.a, page B2-136. */
> +	clean_dcache_pou(code);
> +	dsb(ish);
> +	inval_icache_pou(code);
> +	dsb(ish);
> +	isb();
> +
> +	((fn_t)code)();
> +}
> +
> +static void check_code_generation(bool dcache_clean, bool icache_inval)
> +{
> +	u32 fn[] = {MOV_X0(0x42), RET};
> +	u32 *code = alloc_page();
> +	unsigned long sctlr;
> +	int i, ret;
> +	bool success;
> +
> +	/* Make sure we can execute from a writable page */
> +	mmu_clear_user((unsigned long)code);
> +
> +	sctlr = read_sysreg(sctlr_el1);
> +	if (sctlr & SCTLR_EL1_WXN) {
> +		sctlr &= ~SCTLR_EL1_WXN;
> +		write_sysreg(sctlr, sctlr_el1);
> +		isb();
> +		/* SCTLR_EL1.WXN is permitted to be cached in a TLB. */
> +		flush_tlb_all();
> +	}
> +
> +	for (i = 0; i < ARRAY_SIZE(fn); i++) {
> +		*(code + i) = fn[i];
> +		clean_dcache_pou(code + i);
> +		dsb(ish);
> +		inval_icache_pou(code + i);
> +	}
> +	dsb(ish);
> +	isb();
> +
> +	/* Sanity check */
> +	((fn_t)code)();
> +
> +	success = true;
> +	for (i = 0; i < NTIMES; i++) {
> +		prime_icache(code, MOV_X0(0x42));
> +		*code = MOV_X0(0x66);
> +		if (dcache_clean)
> +			clean_dcache_pou(code);
> +		if (icache_inval) {
> +			if (dcache_clean)
> +				dsb(ish);
> +			inval_icache_pou(code);
> +		}
> +		dsb(ish);
> +		isb();
> +
> +		ret = ((fn_t)code)();
> +		success &= (ret == 0x66);
> +	}
> +
> +	report("code generation", success);
> +}
> +
> +int main(int argc, char **argv)
> +{
> +	u64 ctr, clidr;
> +	bool dcache_clean, icache_inval;
> +
> +	report_prefix_push("IDC-DIC");
> +
> +	ctr = read_sysreg(ctr_el0);
> +	dcache_clean = !(ctr & CTR_IDC);
> +	icache_inval = !(ctr & CTR_DIC);
> +
> +	if (dcache_clean) {
> +		clidr = read_sysreg(clidr_el1);
> +		if ((clidr & CLIDR_LOC_MASK) == 0)
> +			dcache_clean = false;
> +		if ((clidr & CLIDR_LOUU_MASK) == 0 &&
> +		    (clidr & CLIDR_LOUIS_MASK) == 0)
> +			dcache_clean = false;
> +	}
> +
> +	if (dcache_clean)
> +		report_info("dcache clean to PoU required");
> +	if (icache_inval)
> +		report_info("icache invalidation to PoU required");
> +
> +	check_code_generation(dcache_clean, icache_inval);
> +
> +	return report_summary();
> +}
> diff --git a/arm/unittests.cfg b/arm/unittests.cfg
> index 6d3df92a4e28..37f07788c5f0 100644
> --- a/arm/unittests.cfg
> +++ b/arm/unittests.cfg
> @@ -142,3 +142,9 @@ smp = 2
>  groups = nodefault,micro-bench
>  accel = kvm
>  arch = arm64
> +
> +# Cache emulation tests
> +[cache]
> +file = cache.flat
> +arch = arm64
> +group = cache

s/group/groups/

Besides this 'groups' typo

Reviewed-by: Andrew Jones <drjones@redhat.com>
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