RE: [PATCH v4 3/4] makedumpfile/arm64: Add support for ARMv8.2-LVA (52-bit kernel VA support)

[Kazuhito Hagio <k-hagio@ab.jp.nec.com>]

> -----Original Message-----
> > -----Original Message-----
> > With ARMv8.2-LVA architecture extension availability, arm64 hardware
> > which supports this extension can support upto 52-bit virtual
> > addresses. It is specially useful for having a 52-bit user-space virtual
> > address space while the kernel can still retain 48-bit/52-bit virtual
> > addressing.
> >
> > Since at the moment we enable the support of this extension in the
> > kernel via a CONFIG flag (CONFIG_ARM64_VA_BITS_52), so there are
> > no clear mechanisms in user-space to determine this CONFIG
> > flag value and use it to determine the kernel-space VA address range
> > values.
> >
> > 'makedumpfile' can instead use 'TCR_EL1.T1SZ' value from vmcoreinfo
> > which indicates the size offset of the memory region addressed by
> > TTBR1_EL1 (and hence can be used for determining the
> > vabits_actual value).
> >
> > The user-space computation for determining whether an address lies in
> > the linear map range is the same as we have in kernel-space:
> >
> >   #define __is_lm_address(addr)	(!(((u64)addr) & BIT(vabits_actual - 1)))
> >
> > I have sent a kernel patch upstream to add 'TCR_EL1.T1SZ' to
> > vmcoreinfo for arm64 (see [0]).
> >
> > This patch is in accordance with ARMv8 Architecture Reference Manual
> > version D.a
> >
> > Note that with these changes the '--mem-usage' option will not work
> > properly for arm64 (a subsequent patch in this series will address the
> > same) and there is a discussion on-going with the arm64 maintainers to
> > find a way-out for the same (via standard kernel symbols like _stext).
> >
> > [0].http://lists.infradead.org/pipermail/kexec/2019-November/023962.html
> >
> > Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
> > Cc: John Donnelly <john.p.donnelly@oracle.com>
> > Cc: kexec@lists.infradead.org
> > Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
> > ---
> >  arch/arm64.c   | 148 +++++++++++++++++++++++++++++++++++++++++++++------------
> >  makedumpfile.c |   2 +
> >  makedumpfile.h |   3 +-
> >  3 files changed, 122 insertions(+), 31 deletions(-)
> >
> > diff --git a/arch/arm64.c b/arch/arm64.c
> > index ecb19139e178..094d73b8a60f 100644
> > --- a/arch/arm64.c
> > +++ b/arch/arm64.c
> > @@ -47,6 +47,7 @@ typedef struct {
> >  static int lpa_52_bit_support_available;
> >  static int pgtable_level;
> >  static int va_bits;
> > +static int vabits_actual;
> >  static unsigned long kimage_voffset;
> >
> >  #define SZ_4K			4096
> > @@ -218,12 +219,19 @@ pmd_page_paddr(pmd_t pmd)
> >  #define pte_index(vaddr) 		(((vaddr) >> PAGESHIFT()) & (PTRS_PER_PTE - 1))
> >  #define pte_offset(dir, vaddr) 		(pmd_page_paddr((*dir)) + pte_index(vaddr) * sizeof(pte_t))
> >
> > +/*
> > + * The linear kernel range starts at the bottom of the virtual address
> > + * space. Testing the top bit for the start of the region is a
> > + * sufficient check and avoids having to worry about the tag.
> > + */
> > +#define is_linear_addr(addr)	(!(((unsigned long)addr) & (1UL << (vabits_actual - 1))))
> 
> Does this check cover 5.3 or earlier kernels?
> There is no case that vabits_actual is zero?

As you know, 14c127c957c1 ("arm64: mm: Flip kernel VA space") changed
the check for linear address:

-#define __is_lm_address(addr)  (!!((addr) & BIT(VA_BITS - 1)))
+#define __is_lm_address(addr)  (!((addr) & BIT(VA_BITS - 1)))

so if we use the same check as kernel has, I think we will need the
former one to support earlier kernels.

> 
> > +
> >  static unsigned long long
> >  __pa(unsigned long vaddr)
> >  {
> >  	if (kimage_voffset == NOT_FOUND_NUMBER ||
> > -			(vaddr >= PAGE_OFFSET))
> > -		return (vaddr - PAGE_OFFSET + info->phys_base);
> > +			is_linear_addr(vaddr))
> > +		return (vaddr + info->phys_base - PAGE_OFFSET);
> >  	else
> >  		return (vaddr - kimage_voffset);
> >  }
> > @@ -253,6 +261,7 @@ static int calculate_plat_config(void)
> >  			(PAGESIZE() == SZ_64K && va_bits == 42)) {
> >  		pgtable_level = 2;
> >  	} else if ((PAGESIZE() == SZ_64K && va_bits == 48) ||
> > +			(PAGESIZE() == SZ_64K && va_bits == 52) ||
> >  			(PAGESIZE() == SZ_4K && va_bits == 39) ||
> >  			(PAGESIZE() == SZ_16K && va_bits == 47)) {
> >  		pgtable_level = 3;
> > @@ -287,6 +296,16 @@ get_phys_base_arm64(void)
> >  		return TRUE;
> >  	}
> >
> > +	/* If both vabits_actual and va_bits are now initialized, always
> > +	 * prefer vabits_actual over va_bits to calculate PAGE_OFFSET
> > +	 * value.
> > +	 */
> > +	if (vabits_actual && va_bits && vabits_actual != va_bits) {
> > +		info->page_offset = (-(1UL << vabits_actual));
> > +		DEBUG_MSG("page_offset    : %lx (via vabits_actual)\n",
> > +				info->page_offset);
> > +	}
> > +
> 
> Is this for --mem-usage?
> If so, let's drop from this patch and think about it later because
> some additional base functions will be needed for the option, I think.
> 
> >  	if (get_num_pt_loads() && PAGE_OFFSET) {
> >  		for (i = 0;
> >  		    get_pt_load(i, &phys_start, NULL, &virt_start, NULL);
> > @@ -406,6 +425,73 @@ get_stext_symbol(void)
> >  	return(found ? kallsym : FALSE);
> >  }
> >
> > +static int
> > +get_va_bits_from_stext_arm64(void)
> > +{
> > +	ulong _stext;
> > +
> > +	_stext = get_stext_symbol();
> > +	if (!_stext) {
> > +		ERRMSG("Can't get the symbol of _stext.\n");
> > +		return FALSE;
> > +	}
> > +
> > +	/* Derive va_bits as per arch/arm64/Kconfig. Note that this is a
> > +	 * best case approximation at the moment, as there can be
> > +	 * inconsistencies in this calculation (for e.g., for
> > +	 * 52-bit kernel VA case, even the 48th bit might be set in
> > +	 * the _stext symbol).
> > +	 *
> > +	 * So, we need to rely on the actual VA_BITS symbol in the
> > +	 * vmcoreinfo for a accurate value.
> > +	 *
> > +	 * TODO: Improve this further once there is a closure with arm64
> > +	 * kernel maintainers on the same.
> > +	 */
> > +	if ((_stext & PAGE_OFFSET_52) == PAGE_OFFSET_52) {
> > +		va_bits = 52;
> > +	} else if ((_stext & PAGE_OFFSET_48) == PAGE_OFFSET_48) {
> > +		va_bits = 48;
> > +	} else if ((_stext & PAGE_OFFSET_47) == PAGE_OFFSET_47) {
> > +		va_bits = 47;
> > +	} else if ((_stext & PAGE_OFFSET_42) == PAGE_OFFSET_42) {
> > +		va_bits = 42;
> > +	} else if ((_stext & PAGE_OFFSET_39) == PAGE_OFFSET_39) {
> > +		va_bits = 39;
> > +	} else if ((_stext & PAGE_OFFSET_36) == PAGE_OFFSET_36) {
> > +		va_bits = 36;
> > +	} else {
> > +		ERRMSG("Cannot find a proper _stext for calculating VA_BITS\n");
> > +		return FALSE;
> > +	}
> > +
> > +	DEBUG_MSG("va_bits    : %d (_stext) (approximation)\n", va_bits);
> > +
> > +	return TRUE;
> > +}
> > +
> > +static void
> > +get_page_offset_arm64(void)
> > +{
> > +	/* Check if 'vabits_actual' is initialized yet.
> > +	 * If not, our best bet is to use 'va_bits' to calculate
> > +	 * the PAGE_OFFSET value, otherwise use 'vabits_actual'
> > +	 * for the same.
> > +	 *
> > +	 * See arch/arm64/include/asm/memory.h for more details.
> > +	 */
> > +	if (!vabits_actual) {
> > +		info->page_offset = (-(1UL << va_bits));
> > +		DEBUG_MSG("page_offset    : %lx (approximation)\n",
> > +					info->page_offset);
> > +	} else {
> > +		info->page_offset = (-(1UL << vabits_actual));
> > +		DEBUG_MSG("page_offset    : %lx (accurate)\n",
> > +					info->page_offset);
> > +	}
> 
> Does this support 5.3 or earlier kernels?

Because I didn't see the old page_offset calculation below in this patch:

> > -	info->page_offset = (0xffffffffffffffffUL) << (va_bits - 1);

I was thinking that if there is a NUMBER(tcr_el1_t1sz) in vmcoreinfo,
we assume the kernel has the 'flipped' VA space.  And if there is no
NUMBER(tcr_el1_t1sz), then older 'non-flipped' VA [1].

This might be a bit fragile against backport, but it requires less
vmcoreinfo, and older kernels don't need NUMBER(tcr_el1_t1sz).
(they might need NUMBER(MAX_USER_VA_BITS) like RHEL8 though.)

What do you think?

[1] https://github.com/k-hagio/makedumpfile/commit/fd9d86ea05b38e9edbb8c0ac3ebd612d5d485df3#diff-73f1cf659e8099a2f3a94f38063f97ecR400

Thanks,
Kazu


> 
> Thanks,
> Kazu
> 
> > +
> > +}
> > +
> >  int
> >  get_machdep_info_arm64(void)
> >  {
> > @@ -420,8 +506,33 @@ get_machdep_info_arm64(void)
> >  	/* Check if va_bits is still not initialized. If still 0, call
> >  	 * get_versiondep_info() to initialize the same.
> >  	 */
> > +	if (NUMBER(VA_BITS) != NOT_FOUND_NUMBER) {
> > +		va_bits = NUMBER(VA_BITS);
> > +		DEBUG_MSG("va_bits        : %d (vmcoreinfo)\n",
> > +				va_bits);
> > +	}
> > +
> > +	/* Check if va_bits is still not initialized. If still 0, call
> > +	 * get_versiondep_info() to initialize the same from _stext
> > +	 * symbol.
> > +	 */
> >  	if (!va_bits)
> > -		get_versiondep_info_arm64();
> > +		if (get_va_bits_from_stext_arm64() == FALSE)
> > +			return FALSE;
> > +
> > +	get_page_offset_arm64();
> > +
> > +	/* See TCR_EL1, Translation Control Register (EL1) register
> > +	 * description in the ARMv8 Architecture Reference Manual.
> > +	 * Basically, we can use the TCR_EL1.T1SZ
> > +	 * value to determine the virtual addressing range supported
> > +	 * in the kernel-space (i.e. vabits_actual).
> > +	 */
> > +	if (NUMBER(tcr_el1_t1sz) != NOT_FOUND_NUMBER) {
> > +		vabits_actual = 64 - NUMBER(tcr_el1_t1sz);
> > +		DEBUG_MSG("vabits_actual  : %d (vmcoreinfo)\n",
> > +				vabits_actual);
> > +	}
> >
> >  	if (!calculate_plat_config()) {
> >  		ERRMSG("Can't determine platform config values\n");
> > @@ -459,34 +570,11 @@ get_xen_info_arm64(void)
> >  int
> >  get_versiondep_info_arm64(void)
> >  {
> > -	ulong _stext;
> > -
> > -	_stext = get_stext_symbol();
> > -	if (!_stext) {
> > -		ERRMSG("Can't get the symbol of _stext.\n");
> > -		return FALSE;
> > -	}
> > -
> > -	/* Derive va_bits as per arch/arm64/Kconfig */
> > -	if ((_stext & PAGE_OFFSET_36) == PAGE_OFFSET_36) {
> > -		va_bits = 36;
> > -	} else if ((_stext & PAGE_OFFSET_39) == PAGE_OFFSET_39) {
> > -		va_bits = 39;
> > -	} else if ((_stext & PAGE_OFFSET_42) == PAGE_OFFSET_42) {
> > -		va_bits = 42;
> > -	} else if ((_stext & PAGE_OFFSET_47) == PAGE_OFFSET_47) {
> > -		va_bits = 47;
> > -	} else if ((_stext & PAGE_OFFSET_48) == PAGE_OFFSET_48) {
> > -		va_bits = 48;
> > -	} else {
> > -		ERRMSG("Cannot find a proper _stext for calculating VA_BITS\n");
> > -		return FALSE;
> > -	}
> > -
> > -	info->page_offset = (0xffffffffffffffffUL) << (va_bits - 1);
> > +	if (!va_bits)
> > +		if (get_va_bits_from_stext_arm64() == FALSE)
> > +			return FALSE;
> >
> > -	DEBUG_MSG("va_bits      : %d\n", va_bits);
> > -	DEBUG_MSG("page_offset  : %lx\n", info->page_offset);
> > +	get_page_offset_arm64();
> >
> >  	return TRUE;
> >  }
> > diff --git a/makedumpfile.c b/makedumpfile.c
> > index 4a000112ba59..baf559e4d74e 100644
> > --- a/makedumpfile.c
> > +++ b/makedumpfile.c
> > @@ -2314,6 +2314,7 @@ write_vmcoreinfo_data(void)
> >  	WRITE_NUMBER("HUGETLB_PAGE_DTOR", HUGETLB_PAGE_DTOR);
> >  #ifdef __aarch64__
> >  	WRITE_NUMBER("VA_BITS", VA_BITS);
> > +	WRITE_NUMBER_UNSIGNED("tcr_el1_t1sz", tcr_el1_t1sz);
> >  	WRITE_NUMBER_UNSIGNED("PHYS_OFFSET", PHYS_OFFSET);
> >  	WRITE_NUMBER_UNSIGNED("kimage_voffset", kimage_voffset);
> >  #endif
> > @@ -2720,6 +2721,7 @@ read_vmcoreinfo(void)
> >  	READ_NUMBER("KERNEL_IMAGE_SIZE", KERNEL_IMAGE_SIZE);
> >  #ifdef __aarch64__
> >  	READ_NUMBER("VA_BITS", VA_BITS);
> > +	READ_NUMBER_UNSIGNED("tcr_el1_t1sz", tcr_el1_t1sz);
> >  	READ_NUMBER_UNSIGNED("PHYS_OFFSET", PHYS_OFFSET);
> >  	READ_NUMBER_UNSIGNED("kimage_voffset", kimage_voffset);
> >  #endif
> > diff --git a/makedumpfile.h b/makedumpfile.h
> > index ac11e906b5b7..7eab6507c8df 100644
> > --- a/makedumpfile.h
> > +++ b/makedumpfile.h
> > @@ -974,7 +974,7 @@ int get_versiondep_info_arm64(void);
> >  int get_xen_basic_info_arm64(void);
> >  int get_xen_info_arm64(void);
> >  unsigned long get_kaslr_offset_arm64(unsigned long vaddr);
> > -#define paddr_to_vaddr_arm64(X) (((X) - info->phys_base) | PAGE_OFFSET)
> > +#define paddr_to_vaddr_arm64(X) (((X) - (info->phys_base - PAGE_OFFSET)))
> >
> >  #define find_vmemmap()		stub_false()
> >  #define vaddr_to_paddr(X)	vaddr_to_paddr_arm64(X)
> > @@ -1937,6 +1937,7 @@ struct number_table {
> >  	long	KERNEL_IMAGE_SIZE;
> >  #ifdef __aarch64__
> >  	long 	VA_BITS;
> > +	unsigned long	tcr_el1_t1sz;
> >  	unsigned long	PHYS_OFFSET;
> >  	unsigned long	kimage_voffset;
> >  #endif
> > --
> > 2.7.4
> >



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