Re: [PATCH v5] mmap_vmcore: skip non-ram pages reported by hypervisors
"HATAYAMA, Daisuke" writes: > (2014/07/14 18:16), Vitaly Kuznetsov wrote: >> We have a special check in read_vmcore() handler to check if the page was >> reported as ram or not by the hypervisor (pfn_is_ram()). However, when >> vmcore is read with mmap() no such check is performed. That can lead to >> unpredictable results, e.g. when running Xen PVHVM guest memcpy() after >> mmap() on /proc/vmcore will hang processing HVMMEM_mmio_dm pages creating >> enormous load in both DomU and Dom0. >> >> Fix the issue by mapping each non-ram page to the zero page. Keep direct >> path with remap_oldmem_pfn_range() to avoid looping through all pages on >> bare metal. >> >> The issue can also be solved by overriding remap_oldmem_pfn_range() in >> xen-specific code, as remap_oldmem_pfn_range() was been designed for. >> That, however, would involve non-obvious xen code path for all x86 builds >> with CONFIG_XEN_PVHVM=y and would prevent all other hypervisor-specific >> code on x86 arch from doing the same override. >> >> Changes from v4: >> - change map_size type size_t -> unsigned long >> - use prot instead of vma->vm_page_prot inside remap_oldmem_pfn_checked() >> >> Changes from v3: >> - multi line comment style changes >> - minor code style changes >> >> Changes from v2: >> - make remap_oldmem_pfn_checked() interface exactly match >>remap_oldmem_pfn_range() >> - unmap mapped part inside remap_oldmem_pfn_checked() in case of failure so >>we don't need to take care of it in mmap_vmcore() >> - create vmcore_remap_oldmem_pfn() wrapper >> >> Changes from v1: >> - comment style changes >> - change remap_oldmem_pfn_checked() interface to closer match the >>remap_oldmem_pfn() interface >> - preserve formal parameters within the loop, make the loop conditions >>easier to understand >> - use my_zero_pfn() for the zero page >> - return remapped length instead of new offset >> >> Reviewed-by: Andrew Jones >> Signed-off-by: Vitaly Kuznetsov >> --- >> fs/proc/vmcore.c | 83 >> ++-- >> 1 file changed, 80 insertions(+), 3 deletions(-) >> >> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c >> index 382aa89..1f77f35 100644 >> --- a/fs/proc/vmcore.c >> +++ b/fs/proc/vmcore.c >> @@ -328,6 +328,83 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz) >>* virtually contiguous user-space in ELF layout. >>*/ >> #ifdef CONFIG_MMU >> +/* >> + * remap_oldmem_pfn_checked - do remap_oldmem_pfn_range replacing all pages >> + * reported as not being ram with the zero page. >> + * >> + * @vma: vm_area_struct describing requested mapping >> + * @from: start remapping from >> + * @pfn: page frame number to start remapping to >> + * @size: remapping size >> + * @prot: protection bits >> + * >> + * Returns zero on success, -EAGAIN on failure. >> + */ >> +int remap_oldmem_pfn_checked(struct vm_area_struct *vma, unsigned long from, >> + unsigned long pfn, unsigned long size, >> + pgprot_t prot) >> +{ >> +unsigned long map_size; >> +unsigned long pos_start, pos_end, pos; >> +unsigned long zeropage_pfn = my_zero_pfn(0); >> +u64 len = 0; > > Sorry, I missed this yesterday. Thanks for your review! > This should also be fixed as size_t or unsigned long. > Does 32-bit compiler warn about this at the call of do_munmap() below > due to difference of bit length of the two types? Mine doesn't. But you're right, it makes sense to make it match do_munmap()'s interface and len there is size_t. I'll send v6 with this change. > >> + >> +pos_start = pfn; >> +pos_end = pfn + (size >> PAGE_SHIFT); >> + >> +for (pos = pos_start; pos < pos_end; ++pos) { >> +if (!pfn_is_ram(pos)) { >> +/* >> + * We hit a page which is not ram. Remap the continuous >> + * region between pos_start and pos-1 and replace >> + * the non-ram page at pos with the zero page. >> + */ >> +if (pos > pos_start) { >> +/* Remap continuous region */ >> +map_size = (pos - pos_start) << PAGE_SHIFT; >> +if (remap_oldmem_pfn_range(vma, from + len, >> + pos_start, map_size, >> + prot)) >> +goto fail; >> +len += map_size; >> +} >> +/* Remap the zero page */ >> +if (remap_oldmem_pfn_range(vma, from + len, >> + zeropage_pfn, >> + PAGE_SIZE, prot)) >> +goto fail; >> +len += PAGE_SIZE; >> +pos_start = pos + 1; >> +} >> +} >> +
Re: [PATCH v5] mmap_vmcore: skip non-ram pages reported by hypervisors
(2014/07/14 18:16), Vitaly Kuznetsov wrote: > We have a special check in read_vmcore() handler to check if the page was > reported as ram or not by the hypervisor (pfn_is_ram()). However, when > vmcore is read with mmap() no such check is performed. That can lead to > unpredictable results, e.g. when running Xen PVHVM guest memcpy() after > mmap() on /proc/vmcore will hang processing HVMMEM_mmio_dm pages creating > enormous load in both DomU and Dom0. > > Fix the issue by mapping each non-ram page to the zero page. Keep direct > path with remap_oldmem_pfn_range() to avoid looping through all pages on > bare metal. > > The issue can also be solved by overriding remap_oldmem_pfn_range() in > xen-specific code, as remap_oldmem_pfn_range() was been designed for. > That, however, would involve non-obvious xen code path for all x86 builds > with CONFIG_XEN_PVHVM=y and would prevent all other hypervisor-specific > code on x86 arch from doing the same override. > > Changes from v4: > - change map_size type size_t -> unsigned long > - use prot instead of vma->vm_page_prot inside remap_oldmem_pfn_checked() > > Changes from v3: > - multi line comment style changes > - minor code style changes > > Changes from v2: > - make remap_oldmem_pfn_checked() interface exactly match >remap_oldmem_pfn_range() > - unmap mapped part inside remap_oldmem_pfn_checked() in case of failure so >we don't need to take care of it in mmap_vmcore() > - create vmcore_remap_oldmem_pfn() wrapper > > Changes from v1: > - comment style changes > - change remap_oldmem_pfn_checked() interface to closer match the >remap_oldmem_pfn() interface > - preserve formal parameters within the loop, make the loop conditions >easier to understand > - use my_zero_pfn() for the zero page > - return remapped length instead of new offset > > Reviewed-by: Andrew Jones > Signed-off-by: Vitaly Kuznetsov > --- > fs/proc/vmcore.c | 83 > ++-- > 1 file changed, 80 insertions(+), 3 deletions(-) > > diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c > index 382aa89..1f77f35 100644 > --- a/fs/proc/vmcore.c > +++ b/fs/proc/vmcore.c > @@ -328,6 +328,83 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz) >* virtually contiguous user-space in ELF layout. >*/ > #ifdef CONFIG_MMU > +/* > + * remap_oldmem_pfn_checked - do remap_oldmem_pfn_range replacing all pages > + * reported as not being ram with the zero page. > + * > + * @vma: vm_area_struct describing requested mapping > + * @from: start remapping from > + * @pfn: page frame number to start remapping to > + * @size: remapping size > + * @prot: protection bits > + * > + * Returns zero on success, -EAGAIN on failure. > + */ > +int remap_oldmem_pfn_checked(struct vm_area_struct *vma, unsigned long from, > + unsigned long pfn, unsigned long size, > + pgprot_t prot) > +{ > + unsigned long map_size; > + unsigned long pos_start, pos_end, pos; > + unsigned long zeropage_pfn = my_zero_pfn(0); > + u64 len = 0; Sorry, I missed this yesterday. This should also be fixed as size_t or unsigned long. Does 32-bit compiler warn about this at the call of do_munmap() below due to difference of bit length of the two types? > + > + pos_start = pfn; > + pos_end = pfn + (size >> PAGE_SHIFT); > + > + for (pos = pos_start; pos < pos_end; ++pos) { > + if (!pfn_is_ram(pos)) { > + /* > + * We hit a page which is not ram. Remap the continuous > + * region between pos_start and pos-1 and replace > + * the non-ram page at pos with the zero page. > + */ > + if (pos > pos_start) { > + /* Remap continuous region */ > + map_size = (pos - pos_start) << PAGE_SHIFT; > + if (remap_oldmem_pfn_range(vma, from + len, > +pos_start, map_size, > +prot)) > + goto fail; > + len += map_size; > + } > + /* Remap the zero page */ > + if (remap_oldmem_pfn_range(vma, from + len, > +zeropage_pfn, > +PAGE_SIZE, prot)) > + goto fail; > + len += PAGE_SIZE; > + pos_start = pos + 1; > + } > + } > + if (pos > pos_start) { > + /* Remap the rest */ > + map_size = (pos - pos_start) << PAGE_SHIFT; > + if (remap_oldmem_pfn_range(vma, from + len, pos_start, > +map_size, prot)) > + goto
Re: [PATCH v5] mmap_vmcore: skip non-ram pages reported by hypervisors
(2014/07/14 18:16), Vitaly Kuznetsov wrote: We have a special check in read_vmcore() handler to check if the page was reported as ram or not by the hypervisor (pfn_is_ram()). However, when vmcore is read with mmap() no such check is performed. That can lead to unpredictable results, e.g. when running Xen PVHVM guest memcpy() after mmap() on /proc/vmcore will hang processing HVMMEM_mmio_dm pages creating enormous load in both DomU and Dom0. Fix the issue by mapping each non-ram page to the zero page. Keep direct path with remap_oldmem_pfn_range() to avoid looping through all pages on bare metal. The issue can also be solved by overriding remap_oldmem_pfn_range() in xen-specific code, as remap_oldmem_pfn_range() was been designed for. That, however, would involve non-obvious xen code path for all x86 builds with CONFIG_XEN_PVHVM=y and would prevent all other hypervisor-specific code on x86 arch from doing the same override. Changes from v4: - change map_size type size_t - unsigned long - use prot instead of vma-vm_page_prot inside remap_oldmem_pfn_checked() Changes from v3: - multi line comment style changes - minor code style changes Changes from v2: - make remap_oldmem_pfn_checked() interface exactly match remap_oldmem_pfn_range() - unmap mapped part inside remap_oldmem_pfn_checked() in case of failure so we don't need to take care of it in mmap_vmcore() - create vmcore_remap_oldmem_pfn() wrapper Changes from v1: - comment style changes - change remap_oldmem_pfn_checked() interface to closer match the remap_oldmem_pfn() interface - preserve formal parameters within the loop, make the loop conditions easier to understand - use my_zero_pfn() for the zero page - return remapped length instead of new offset Reviewed-by: Andrew Jones drjo...@redhat.com Signed-off-by: Vitaly Kuznetsov vkuzn...@redhat.com --- fs/proc/vmcore.c | 83 ++-- 1 file changed, 80 insertions(+), 3 deletions(-) diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index 382aa89..1f77f35 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -328,6 +328,83 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz) * virtually contiguous user-space in ELF layout. */ #ifdef CONFIG_MMU +/* + * remap_oldmem_pfn_checked - do remap_oldmem_pfn_range replacing all pages + * reported as not being ram with the zero page. + * + * @vma: vm_area_struct describing requested mapping + * @from: start remapping from + * @pfn: page frame number to start remapping to + * @size: remapping size + * @prot: protection bits + * + * Returns zero on success, -EAGAIN on failure. + */ +int remap_oldmem_pfn_checked(struct vm_area_struct *vma, unsigned long from, + unsigned long pfn, unsigned long size, + pgprot_t prot) +{ + unsigned long map_size; + unsigned long pos_start, pos_end, pos; + unsigned long zeropage_pfn = my_zero_pfn(0); + u64 len = 0; Sorry, I missed this yesterday. This should also be fixed as size_t or unsigned long. Does 32-bit compiler warn about this at the call of do_munmap() below due to difference of bit length of the two types? + + pos_start = pfn; + pos_end = pfn + (size PAGE_SHIFT); + + for (pos = pos_start; pos pos_end; ++pos) { + if (!pfn_is_ram(pos)) { + /* + * We hit a page which is not ram. Remap the continuous + * region between pos_start and pos-1 and replace + * the non-ram page at pos with the zero page. + */ + if (pos pos_start) { + /* Remap continuous region */ + map_size = (pos - pos_start) PAGE_SHIFT; + if (remap_oldmem_pfn_range(vma, from + len, +pos_start, map_size, +prot)) + goto fail; + len += map_size; + } + /* Remap the zero page */ + if (remap_oldmem_pfn_range(vma, from + len, +zeropage_pfn, +PAGE_SIZE, prot)) + goto fail; + len += PAGE_SIZE; + pos_start = pos + 1; + } + } + if (pos pos_start) { + /* Remap the rest */ + map_size = (pos - pos_start) PAGE_SHIFT; + if (remap_oldmem_pfn_range(vma, from + len, pos_start, +map_size, prot)) + goto fail; + len += map_size; + } + return 0; +fail: +
Re: [PATCH v5] mmap_vmcore: skip non-ram pages reported by hypervisors
HATAYAMA, Daisuke d.hatay...@jp.fujitsu.com writes: (2014/07/14 18:16), Vitaly Kuznetsov wrote: We have a special check in read_vmcore() handler to check if the page was reported as ram or not by the hypervisor (pfn_is_ram()). However, when vmcore is read with mmap() no such check is performed. That can lead to unpredictable results, e.g. when running Xen PVHVM guest memcpy() after mmap() on /proc/vmcore will hang processing HVMMEM_mmio_dm pages creating enormous load in both DomU and Dom0. Fix the issue by mapping each non-ram page to the zero page. Keep direct path with remap_oldmem_pfn_range() to avoid looping through all pages on bare metal. The issue can also be solved by overriding remap_oldmem_pfn_range() in xen-specific code, as remap_oldmem_pfn_range() was been designed for. That, however, would involve non-obvious xen code path for all x86 builds with CONFIG_XEN_PVHVM=y and would prevent all other hypervisor-specific code on x86 arch from doing the same override. Changes from v4: - change map_size type size_t - unsigned long - use prot instead of vma-vm_page_prot inside remap_oldmem_pfn_checked() Changes from v3: - multi line comment style changes - minor code style changes Changes from v2: - make remap_oldmem_pfn_checked() interface exactly match remap_oldmem_pfn_range() - unmap mapped part inside remap_oldmem_pfn_checked() in case of failure so we don't need to take care of it in mmap_vmcore() - create vmcore_remap_oldmem_pfn() wrapper Changes from v1: - comment style changes - change remap_oldmem_pfn_checked() interface to closer match the remap_oldmem_pfn() interface - preserve formal parameters within the loop, make the loop conditions easier to understand - use my_zero_pfn() for the zero page - return remapped length instead of new offset Reviewed-by: Andrew Jones drjo...@redhat.com Signed-off-by: Vitaly Kuznetsov vkuzn...@redhat.com --- fs/proc/vmcore.c | 83 ++-- 1 file changed, 80 insertions(+), 3 deletions(-) diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index 382aa89..1f77f35 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -328,6 +328,83 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz) * virtually contiguous user-space in ELF layout. */ #ifdef CONFIG_MMU +/* + * remap_oldmem_pfn_checked - do remap_oldmem_pfn_range replacing all pages + * reported as not being ram with the zero page. + * + * @vma: vm_area_struct describing requested mapping + * @from: start remapping from + * @pfn: page frame number to start remapping to + * @size: remapping size + * @prot: protection bits + * + * Returns zero on success, -EAGAIN on failure. + */ +int remap_oldmem_pfn_checked(struct vm_area_struct *vma, unsigned long from, + unsigned long pfn, unsigned long size, + pgprot_t prot) +{ +unsigned long map_size; +unsigned long pos_start, pos_end, pos; +unsigned long zeropage_pfn = my_zero_pfn(0); +u64 len = 0; Sorry, I missed this yesterday. Thanks for your review! This should also be fixed as size_t or unsigned long. Does 32-bit compiler warn about this at the call of do_munmap() below due to difference of bit length of the two types? Mine doesn't. But you're right, it makes sense to make it match do_munmap()'s interface and len there is size_t. I'll send v6 with this change. + +pos_start = pfn; +pos_end = pfn + (size PAGE_SHIFT); + +for (pos = pos_start; pos pos_end; ++pos) { +if (!pfn_is_ram(pos)) { +/* + * We hit a page which is not ram. Remap the continuous + * region between pos_start and pos-1 and replace + * the non-ram page at pos with the zero page. + */ +if (pos pos_start) { +/* Remap continuous region */ +map_size = (pos - pos_start) PAGE_SHIFT; +if (remap_oldmem_pfn_range(vma, from + len, + pos_start, map_size, + prot)) +goto fail; +len += map_size; +} +/* Remap the zero page */ +if (remap_oldmem_pfn_range(vma, from + len, + zeropage_pfn, + PAGE_SIZE, prot)) +goto fail; +len += PAGE_SIZE; +pos_start = pos + 1; +} +} +if (pos pos_start) { +/* Remap the rest */ +map_size = (pos - pos_start) PAGE_SHIFT; +if (remap_oldmem_pfn_range(vma, from +