[RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Ard Biesheuvel]

We carry a quirk in the x86 EFI code to switch back to an older
method of mapping the EFI runtime services memory regions, because
it was deemed risky at the time to implement a new method without
providing a fallback to the old method in case problems arose.

Such problems did arise, but they appear to be limited to SGI UV1
machines, and so these are the only ones for which the fallback gets
enabled automatically (via a DMI quirk). The fallback can be enabled
manually as well, by passing efi=old_map, but there is very little
evidence that suggests that this is something that is being relied
upon in the field.

Given that UV1 support is not enabled by default by the distros
(Ubuntu, Fedora), there is no point in carrying this fallback code
all the time if there are no other users. So let's refactor it a bit
to make it depend on CONFIG_X86_UV, and remove the ability to enable
it by hand.

Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Cc: Mike Travis <mike.travis@hpe.com>
Cc: Hedi Berriche <hedi.berriche@hpe.com> 
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  5 +---
 arch/x86/include/asm/efi.h                      | 21 ++++++++------
 arch/x86/kernel/kexec-bzimage64.c               |  2 +-
 arch/x86/platform/efi/efi.c                     | 30 ++++----------------
 arch/x86/platform/efi/efi_64.c                  | 18 ++++++------
 arch/x86/platform/efi/quirks.c                  | 11 ++-----
 arch/x86/platform/uv/bios_uv.c                  |  2 +-
 7 files changed, 32 insertions(+), 57 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ade4e6ec23e0..fbcf8d1eb3ee 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1164,11 +1164,8 @@
 			Format: {"off" | "on" | "skip[mbr]"}
 
 	efi=		[EFI]
-			Format: { "old_map", "nochunk", "noruntime", "debug",
+			Format: { "nochunk", "noruntime", "debug",
 				  "nosoftreserve" }
-			old_map [X86-64]: switch to the old ioremap-based EFI
-			runtime services mapping. 32-bit still uses this one by
-			default.
 			nochunk: disable reading files in "chunks" in the EFI
 			boot stub, as chunking can cause problems with some
 			firmware implementations.
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 8f4727a8a658..be40110bbee2 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -19,13 +19,16 @@
  * This is the main reason why we're doing stable VA mappings for RT
  * services.
  *
- * This flag is used in conjunction with a chicken bit called
- * "efi=old_map" which can be used as a fallback to the old runtime
- * services mapping method in case there's some b0rkage with a
- * particular EFI implementation (haha, it is hard to hold up the
- * sarcasm here...).
+ * SGI UV1 machines are known to be incompatible with this scheme, so we
+ * provide an opt-out for these machines via a DMI quirk that sets the
+ * attribute below.
  */
-#define EFI_OLD_MEMMAP		EFI_ARCH_1
+#define EFI_UV1_MEMMAP		EFI_ARCH_1
+
+static inline bool efi_have_uv1_memmap(void)
+{
+	return IS_ENABLED(CONFIG_X86_UV) && efi_enabled(EFI_UV1_MEMMAP);
+}
 
 #define EFI32_LOADER_SIGNATURE	"EL32"
 #define EFI64_LOADER_SIGNATURE	"EL64"
@@ -75,7 +78,7 @@ struct efi_scratch {
 	kernel_fpu_begin();						\
 	firmware_restrict_branch_speculation_start();			\
 									\
-	if (!efi_enabled(EFI_OLD_MEMMAP))				\
+	if (!efi_have_uv1_memmap())					\
 		efi_switch_mm(&efi_mm);					\
 })
 
@@ -84,7 +87,7 @@ struct efi_scratch {
 
 #define arch_efi_call_virt_teardown()					\
 ({									\
-	if (!efi_enabled(EFI_OLD_MEMMAP))				\
+	if (!efi_have_uv1_memmap())					\
 		efi_switch_mm(efi_scratch.prev_mm);			\
 									\
 	firmware_restrict_branch_speculation_end();			\
@@ -156,7 +159,7 @@ static inline bool efi_runtime_supported(void)
 	if (!efi_is_mixed())
 		return true;
 
-	if (!efi_enabled(EFI_OLD_MEMMAP))
+	if (!efi_have_uv1_memmap())
 		return true;
 
 	return false;
diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
index d2f4e706a428..f293d872602a 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -177,7 +177,7 @@ setup_efi_state(struct boot_params *params, unsigned long params_load_addr,
 	 * acpi_rsdp=<addr> on kernel command line to make second kernel boot
 	 * without efi.
 	 */
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		return 0;
 
 	params->secure_boot = boot_params.secure_boot;
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index b14b1c1f21bd..cabaf3de3821 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -789,7 +789,7 @@ static inline void *efi_map_next_entry_reverse(void *entry)
  */
 static void *efi_map_next_entry(void *entry)
 {
-	if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_64BIT)) {
+	if (!efi_have_uv1_memmap() && efi_enabled(EFI_64BIT)) {
 		/*
 		 * Starting in UEFI v2.5 the EFI_PROPERTIES_TABLE
 		 * config table feature requires us to map all entries
@@ -921,11 +921,11 @@ static void __init kexec_enter_virtual_mode(void)
 
 	/*
 	 * We don't do virtual mode, since we don't do runtime services, on
-	 * non-native EFI. With efi=old_map, we don't do runtime services in
+	 * non-native EFI. With UV1 memmap, we don't do runtime services in
 	 * kexec kernel because in the initial boot something else might
 	 * have been mapped at these virtual addresses.
 	 */
-	if (efi_is_mixed() || efi_enabled(EFI_OLD_MEMMAP)) {
+	if (efi_is_mixed() || efi_have_uv1_memmap()) {
 		efi_memmap_unmap();
 		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 		return;
@@ -983,7 +983,7 @@ static void __init kexec_enter_virtual_mode(void)
 
 	efi.set_virtual_address_map = NULL;
 
-	if (efi_enabled(EFI_OLD_MEMMAP) && (__supported_pte_mask & _PAGE_NX))
+	if (efi_have_uv1_memmap() && (__supported_pte_mask & _PAGE_NX))
 		runtime_code_page_mkexec();
 #endif
 }
@@ -994,13 +994,7 @@ static void __init kexec_enter_virtual_mode(void)
  * has the runtime attribute bit set in its memory descriptor into the
  * efi_pgd page table.
  *
- * The old method which used to update that memory descriptor with the
- * virtual address obtained from ioremap() is still supported when the
- * kernel is booted with efi=old_map on its command line. Same old
- * method enabled the runtime services to be called without having to
- * thunk back into physical mode for every invocation.
- *
- * The new method does a pagetable switch in a preemption-safe manner
+ * This method does a pagetable switch in a preemption-safe manner
  * so that we're in a different address space when calling a runtime
  * function. For function arguments passing we do copy the PUDs of the
  * kernel page table into efi_pgd prior to each call.
@@ -1124,20 +1118,6 @@ void __init efi_enter_virtual_mode(void)
 	efi_dump_pagetable();
 }
 
-static int __init arch_parse_efi_cmdline(char *str)
-{
-	if (!str) {
-		pr_warn("need at least one option\n");
-		return -EINVAL;
-	}
-
-	if (parse_option_str(str, "old_map"))
-		set_bit(EFI_OLD_MEMMAP, &efi.flags);
-
-	return 0;
-}
-early_param("efi", arch_parse_efi_cmdline);
-
 bool efi_is_table_address(unsigned long phys_addr)
 {
 	unsigned int i;
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 3690df1d31c6..aed13d68313b 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -82,7 +82,7 @@ pgd_t * __init efi_call_phys_prolog(void)
 	int pgd;
 	int n_pgds, i, j;
 
-	if (!efi_enabled(EFI_OLD_MEMMAP)) {
+	if (!efi_have_uv1_memmap()) {
 		efi_switch_mm(&efi_mm);
 		kernel_fpu_begin();
 		return efi_mm.pgd;
@@ -96,7 +96,7 @@ pgd_t * __init efi_call_phys_prolog(void)
 		return NULL;
 
 	/*
-	 * Build 1:1 identity mapping for efi=old_map usage. Note that
+	 * Build 1:1 identity mapping for UV1 memmap usage. Note that
 	 * PAGE_OFFSET is PGDIR_SIZE aligned when KASLR is disabled, while
 	 * it is PUD_SIZE ALIGNED with KASLR enabled. So for a given physical
 	 * address X, the pud_index(X) != pud_index(__va(X)), we can only copy
@@ -162,7 +162,7 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
 
 	kernel_fpu_end();
 
-	if (!efi_enabled(EFI_OLD_MEMMAP)) {
+	if (!efi_have_uv1_memmap()) {
 		efi_switch_mm(efi_scratch.prev_mm);
 		return;
 	}
@@ -215,7 +215,7 @@ int __init efi_alloc_page_tables(void)
 	pud_t *pud;
 	gfp_t gfp_mask;
 
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		return 0;
 
 	gfp_mask = GFP_KERNEL | __GFP_ZERO;
@@ -256,7 +256,7 @@ void efi_sync_low_kernel_mappings(void)
 	pud_t *pud_k, *pud_efi;
 	pgd_t *efi_pgd = efi_mm.pgd;
 
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		return;
 
 	/*
@@ -350,7 +350,7 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 	unsigned npages;
 	pgd_t *pgd = efi_mm.pgd;
 
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		return 0;
 
 	/*
@@ -438,7 +438,7 @@ void __init efi_map_region(efi_memory_desc_t *md)
 	unsigned long size = md->num_pages << PAGE_SHIFT;
 	u64 pa = md->phys_addr;
 
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		return old_map_region(md);
 
 	/*
@@ -563,7 +563,7 @@ void __init efi_runtime_update_mappings(void)
 {
 	efi_memory_desc_t *md;
 
-	if (efi_enabled(EFI_OLD_MEMMAP)) {
+	if (efi_have_uv1_memmap()) {
 		if (__supported_pte_mask & _PAGE_NX)
 			runtime_code_page_mkexec();
 		return;
@@ -617,7 +617,7 @@ void __init efi_runtime_update_mappings(void)
 void __init efi_dump_pagetable(void)
 {
 #ifdef CONFIG_EFI_PGT_DUMP
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		ptdump_walk_pgd_level(NULL, swapper_pg_dir);
 	else
 		ptdump_walk_pgd_level(NULL, efi_mm.pgd);
diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index eb421cb35108..b5ce1c41246b 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -382,12 +382,7 @@ static void __init efi_unmap_pages(efi_memory_desc_t *md)
 	u64 pa = md->phys_addr;
 	u64 va = md->virt_addr;
 
-	/*
-	 * To Do: Remove this check after adding functionality to unmap EFI boot
-	 * services code/data regions from direct mapping area because
-	 * "efi=old_map" maps EFI regions in swapper_pg_dir.
-	 */
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		return;
 
 	/*
@@ -582,7 +577,7 @@ void __init efi_apply_memmap_quirks(void)
 
 	/* UV2+ BIOS has a fix for this issue.  UV1 still needs the quirk. */
 	if (dmi_check_system(sgi_uv1_dmi))
-		set_bit(EFI_OLD_MEMMAP, &efi.flags);
+		set_bit(EFI_UV1_MEMMAP, &efi.flags);
 }
 
 /*
@@ -720,7 +715,7 @@ void efi_recover_from_page_fault(unsigned long phys_addr)
 	/*
 	 * Make sure that an efi runtime service caused the page fault.
 	 * "efi_mm" cannot be used to check if the page fault had occurred
-	 * in the firmware context because efi=old_map doesn't use efi_pgd.
+	 * in the firmware context because UV1 memmap doesn't use efi_pgd.
 	 */
 	if (efi_rts_work.efi_rts_id == EFI_NONE)
 		return;
diff --git a/arch/x86/platform/uv/bios_uv.c b/arch/x86/platform/uv/bios_uv.c
index 5c0e2eb5d87c..b6c33deb8f0c 100644
--- a/arch/x86/platform/uv/bios_uv.c
+++ b/arch/x86/platform/uv/bios_uv.c
@@ -34,7 +34,7 @@ static s64 __uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3,
 	 * If EFI_OLD_MEMMAP is set, we need to fall back to using our old EFI
 	 * callback method, which uses efi_call() directly, with the kernel page tables:
 	 */
-	if (unlikely(efi_enabled(EFI_OLD_MEMMAP))) {
+	if (unlikely(efi_enabled(EFI_UV1_MEMMAP))) {
 		kernel_fpu_begin();
 		ret = efi_call((void *)__va(tab->function), (u64)which, a1, a2, a3, a4, a5);
 		kernel_fpu_end();
-- 
2.17.1

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Ard Biesheuvel]

(adding Boris and Dave for the historical perspective)

On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> We carry a quirk in the x86 EFI code to switch back to an older
> method of mapping the EFI runtime services memory regions, because
> it was deemed risky at the time to implement a new method without
> providing a fallback to the old method in case problems arose.
>
> Such problems did arise, but they appear to be limited to SGI UV1
> machines, and so these are the only ones for which the fallback gets
> enabled automatically (via a DMI quirk). The fallback can be enabled
> manually as well, by passing efi=old_map, but there is very little
> evidence that suggests that this is something that is being relied
> upon in the field.
>
> Given that UV1 support is not enabled by default by the distros
> (Ubuntu, Fedora), there is no point in carrying this fallback code
> all the time if there are no other users. So let's refactor it a bit
> to make it depend on CONFIG_X86_UV, and remove the ability to enable
> it by hand.
>
> Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> Cc: Mike Travis <mike.travis@hpe.com>
> Cc: Hedi Berriche <hedi.berriche@hpe.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Boris, since you were the one that added efi=old_map: do you know of
any cases beyond SGI UV1 where it was actually needed? There is some
mention of using it to work around transient breakage on 32-bit caused
by your original changes, but other than that, Google doesn't seem to
know about any cases where efi=old_map is being used to deal with
actual firmware quirks.

As a followup to this change, I'd like to move the old memmap handling
into the UV1 support code, so it is omitted unless UV support is
compiled it, and so it can be retired with the rest of it once that
time comes.



> ---
>  Documentation/admin-guide/kernel-parameters.txt |  5 +---
>  arch/x86/include/asm/efi.h                      | 21 ++++++++------
>  arch/x86/kernel/kexec-bzimage64.c               |  2 +-
>  arch/x86/platform/efi/efi.c                     | 30 ++++----------------
>  arch/x86/platform/efi/efi_64.c                  | 18 ++++++------
>  arch/x86/platform/efi/quirks.c                  | 11 ++-----
>  arch/x86/platform/uv/bios_uv.c                  |  2 +-
>  7 files changed, 32 insertions(+), 57 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index ade4e6ec23e0..fbcf8d1eb3ee 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1164,11 +1164,8 @@
>                         Format: {"off" | "on" | "skip[mbr]"}
>
>         efi=            [EFI]
> -                       Format: { "old_map", "nochunk", "noruntime", "debug",
> +                       Format: { "nochunk", "noruntime", "debug",
>                                   "nosoftreserve" }
> -                       old_map [X86-64]: switch to the old ioremap-based EFI
> -                       runtime services mapping. 32-bit still uses this one by
> -                       default.
>                         nochunk: disable reading files in "chunks" in the EFI
>                         boot stub, as chunking can cause problems with some
>                         firmware implementations.
> diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
> index 8f4727a8a658..be40110bbee2 100644
> --- a/arch/x86/include/asm/efi.h
> +++ b/arch/x86/include/asm/efi.h
> @@ -19,13 +19,16 @@
>   * This is the main reason why we're doing stable VA mappings for RT
>   * services.
>   *
> - * This flag is used in conjunction with a chicken bit called
> - * "efi=old_map" which can be used as a fallback to the old runtime
> - * services mapping method in case there's some b0rkage with a
> - * particular EFI implementation (haha, it is hard to hold up the
> - * sarcasm here...).
> + * SGI UV1 machines are known to be incompatible with this scheme, so we
> + * provide an opt-out for these machines via a DMI quirk that sets the
> + * attribute below.
>   */
> -#define EFI_OLD_MEMMAP         EFI_ARCH_1
> +#define EFI_UV1_MEMMAP         EFI_ARCH_1
> +
> +static inline bool efi_have_uv1_memmap(void)
> +{
> +       return IS_ENABLED(CONFIG_X86_UV) && efi_enabled(EFI_UV1_MEMMAP);
> +}
>
>  #define EFI32_LOADER_SIGNATURE "EL32"
>  #define EFI64_LOADER_SIGNATURE "EL64"
> @@ -75,7 +78,7 @@ struct efi_scratch {
>         kernel_fpu_begin();                                             \
>         firmware_restrict_branch_speculation_start();                   \
>                                                                         \
> -       if (!efi_enabled(EFI_OLD_MEMMAP))                               \
> +       if (!efi_have_uv1_memmap())                                     \
>                 efi_switch_mm(&efi_mm);                                 \
>  })
>
> @@ -84,7 +87,7 @@ struct efi_scratch {
>
>  #define arch_efi_call_virt_teardown()                                  \
>  ({                                                                     \
> -       if (!efi_enabled(EFI_OLD_MEMMAP))                               \
> +       if (!efi_have_uv1_memmap())                                     \
>                 efi_switch_mm(efi_scratch.prev_mm);                     \
>                                                                         \
>         firmware_restrict_branch_speculation_end();                     \
> @@ -156,7 +159,7 @@ static inline bool efi_runtime_supported(void)
>         if (!efi_is_mixed())
>                 return true;
>
> -       if (!efi_enabled(EFI_OLD_MEMMAP))
> +       if (!efi_have_uv1_memmap())
>                 return true;
>
>         return false;
> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
> index d2f4e706a428..f293d872602a 100644
> --- a/arch/x86/kernel/kexec-bzimage64.c
> +++ b/arch/x86/kernel/kexec-bzimage64.c
> @@ -177,7 +177,7 @@ setup_efi_state(struct boot_params *params, unsigned long params_load_addr,
>          * acpi_rsdp=<addr> on kernel command line to make second kernel boot
>          * without efi.
>          */
> -       if (efi_enabled(EFI_OLD_MEMMAP))
> +       if (efi_have_uv1_memmap())
>                 return 0;
>
>         params->secure_boot = boot_params.secure_boot;
> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index b14b1c1f21bd..cabaf3de3821 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -789,7 +789,7 @@ static inline void *efi_map_next_entry_reverse(void *entry)
>   */
>  static void *efi_map_next_entry(void *entry)
>  {
> -       if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_64BIT)) {
> +       if (!efi_have_uv1_memmap() && efi_enabled(EFI_64BIT)) {
>                 /*
>                  * Starting in UEFI v2.5 the EFI_PROPERTIES_TABLE
>                  * config table feature requires us to map all entries
> @@ -921,11 +921,11 @@ static void __init kexec_enter_virtual_mode(void)
>
>         /*
>          * We don't do virtual mode, since we don't do runtime services, on
> -        * non-native EFI. With efi=old_map, we don't do runtime services in
> +        * non-native EFI. With UV1 memmap, we don't do runtime services in
>          * kexec kernel because in the initial boot something else might
>          * have been mapped at these virtual addresses.
>          */
> -       if (efi_is_mixed() || efi_enabled(EFI_OLD_MEMMAP)) {
> +       if (efi_is_mixed() || efi_have_uv1_memmap()) {
>                 efi_memmap_unmap();
>                 clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
>                 return;
> @@ -983,7 +983,7 @@ static void __init kexec_enter_virtual_mode(void)
>
>         efi.set_virtual_address_map = NULL;
>
> -       if (efi_enabled(EFI_OLD_MEMMAP) && (__supported_pte_mask & _PAGE_NX))
> +       if (efi_have_uv1_memmap() && (__supported_pte_mask & _PAGE_NX))
>                 runtime_code_page_mkexec();
>  #endif
>  }
> @@ -994,13 +994,7 @@ static void __init kexec_enter_virtual_mode(void)
>   * has the runtime attribute bit set in its memory descriptor into the
>   * efi_pgd page table.
>   *
> - * The old method which used to update that memory descriptor with the
> - * virtual address obtained from ioremap() is still supported when the
> - * kernel is booted with efi=old_map on its command line. Same old
> - * method enabled the runtime services to be called without having to
> - * thunk back into physical mode for every invocation.
> - *
> - * The new method does a pagetable switch in a preemption-safe manner
> + * This method does a pagetable switch in a preemption-safe manner
>   * so that we're in a different address space when calling a runtime
>   * function. For function arguments passing we do copy the PUDs of the
>   * kernel page table into efi_pgd prior to each call.
> @@ -1124,20 +1118,6 @@ void __init efi_enter_virtual_mode(void)
>         efi_dump_pagetable();
>  }
>
> -static int __init arch_parse_efi_cmdline(char *str)
> -{
> -       if (!str) {
> -               pr_warn("need at least one option\n");
> -               return -EINVAL;
> -       }
> -
> -       if (parse_option_str(str, "old_map"))
> -               set_bit(EFI_OLD_MEMMAP, &efi.flags);
> -
> -       return 0;
> -}
> -early_param("efi", arch_parse_efi_cmdline);
> -
>  bool efi_is_table_address(unsigned long phys_addr)
>  {
>         unsigned int i;
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 3690df1d31c6..aed13d68313b 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -82,7 +82,7 @@ pgd_t * __init efi_call_phys_prolog(void)
>         int pgd;
>         int n_pgds, i, j;
>
> -       if (!efi_enabled(EFI_OLD_MEMMAP)) {
> +       if (!efi_have_uv1_memmap()) {
>                 efi_switch_mm(&efi_mm);
>                 kernel_fpu_begin();
>                 return efi_mm.pgd;
> @@ -96,7 +96,7 @@ pgd_t * __init efi_call_phys_prolog(void)
>                 return NULL;
>
>         /*
> -        * Build 1:1 identity mapping for efi=old_map usage. Note that
> +        * Build 1:1 identity mapping for UV1 memmap usage. Note that
>          * PAGE_OFFSET is PGDIR_SIZE aligned when KASLR is disabled, while
>          * it is PUD_SIZE ALIGNED with KASLR enabled. So for a given physical
>          * address X, the pud_index(X) != pud_index(__va(X)), we can only copy
> @@ -162,7 +162,7 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
>
>         kernel_fpu_end();
>
> -       if (!efi_enabled(EFI_OLD_MEMMAP)) {
> +       if (!efi_have_uv1_memmap()) {
>                 efi_switch_mm(efi_scratch.prev_mm);
>                 return;
>         }
> @@ -215,7 +215,7 @@ int __init efi_alloc_page_tables(void)
>         pud_t *pud;
>         gfp_t gfp_mask;
>
> -       if (efi_enabled(EFI_OLD_MEMMAP))
> +       if (efi_have_uv1_memmap())
>                 return 0;
>
>         gfp_mask = GFP_KERNEL | __GFP_ZERO;
> @@ -256,7 +256,7 @@ void efi_sync_low_kernel_mappings(void)
>         pud_t *pud_k, *pud_efi;
>         pgd_t *efi_pgd = efi_mm.pgd;
>
> -       if (efi_enabled(EFI_OLD_MEMMAP))
> +       if (efi_have_uv1_memmap())
>                 return;
>
>         /*
> @@ -350,7 +350,7 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
>         unsigned npages;
>         pgd_t *pgd = efi_mm.pgd;
>
> -       if (efi_enabled(EFI_OLD_MEMMAP))
> +       if (efi_have_uv1_memmap())
>                 return 0;
>
>         /*
> @@ -438,7 +438,7 @@ void __init efi_map_region(efi_memory_desc_t *md)
>         unsigned long size = md->num_pages << PAGE_SHIFT;
>         u64 pa = md->phys_addr;
>
> -       if (efi_enabled(EFI_OLD_MEMMAP))
> +       if (efi_have_uv1_memmap())
>                 return old_map_region(md);
>
>         /*
> @@ -563,7 +563,7 @@ void __init efi_runtime_update_mappings(void)
>  {
>         efi_memory_desc_t *md;
>
> -       if (efi_enabled(EFI_OLD_MEMMAP)) {
> +       if (efi_have_uv1_memmap()) {
>                 if (__supported_pte_mask & _PAGE_NX)
>                         runtime_code_page_mkexec();
>                 return;
> @@ -617,7 +617,7 @@ void __init efi_runtime_update_mappings(void)
>  void __init efi_dump_pagetable(void)
>  {
>  #ifdef CONFIG_EFI_PGT_DUMP
> -       if (efi_enabled(EFI_OLD_MEMMAP))
> +       if (efi_have_uv1_memmap())
>                 ptdump_walk_pgd_level(NULL, swapper_pg_dir);
>         else
>                 ptdump_walk_pgd_level(NULL, efi_mm.pgd);
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index eb421cb35108..b5ce1c41246b 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -382,12 +382,7 @@ static void __init efi_unmap_pages(efi_memory_desc_t *md)
>         u64 pa = md->phys_addr;
>         u64 va = md->virt_addr;
>
> -       /*
> -        * To Do: Remove this check after adding functionality to unmap EFI boot
> -        * services code/data regions from direct mapping area because
> -        * "efi=old_map" maps EFI regions in swapper_pg_dir.
> -        */
> -       if (efi_enabled(EFI_OLD_MEMMAP))
> +       if (efi_have_uv1_memmap())
>                 return;
>
>         /*
> @@ -582,7 +577,7 @@ void __init efi_apply_memmap_quirks(void)
>
>         /* UV2+ BIOS has a fix for this issue.  UV1 still needs the quirk. */
>         if (dmi_check_system(sgi_uv1_dmi))
> -               set_bit(EFI_OLD_MEMMAP, &efi.flags);
> +               set_bit(EFI_UV1_MEMMAP, &efi.flags);
>  }
>
>  /*
> @@ -720,7 +715,7 @@ void efi_recover_from_page_fault(unsigned long phys_addr)
>         /*
>          * Make sure that an efi runtime service caused the page fault.
>          * "efi_mm" cannot be used to check if the page fault had occurred
> -        * in the firmware context because efi=old_map doesn't use efi_pgd.
> +        * in the firmware context because UV1 memmap doesn't use efi_pgd.
>          */
>         if (efi_rts_work.efi_rts_id == EFI_NONE)
>                 return;
> diff --git a/arch/x86/platform/uv/bios_uv.c b/arch/x86/platform/uv/bios_uv.c
> index 5c0e2eb5d87c..b6c33deb8f0c 100644
> --- a/arch/x86/platform/uv/bios_uv.c
> +++ b/arch/x86/platform/uv/bios_uv.c
> @@ -34,7 +34,7 @@ static s64 __uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3,
>          * If EFI_OLD_MEMMAP is set, we need to fall back to using our old EFI
>          * callback method, which uses efi_call() directly, with the kernel page tables:
>          */
> -       if (unlikely(efi_enabled(EFI_OLD_MEMMAP))) {
> +       if (unlikely(efi_enabled(EFI_UV1_MEMMAP))) {
>                 kernel_fpu_begin();
>                 ret = efi_call((void *)__va(tab->function), (u64)which, a1, a2, a3, a4, a5);
>                 kernel_fpu_end();
> --
> 2.17.1
>

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Borislav Petkov]

On Tue, Dec 31, 2019 at 12:13:18PM +0100, Ard Biesheuvel wrote:
> (adding Boris and Dave for the historical perspective)
> 
> On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > We carry a quirk in the x86 EFI code to switch back to an older
> > method of mapping the EFI runtime services memory regions, because
> > it was deemed risky at the time to implement a new method without
> > providing a fallback to the old method in case problems arose.
> >
> > Such problems did arise, but they appear to be limited to SGI UV1
> > machines, and so these are the only ones for which the fallback gets
> > enabled automatically (via a DMI quirk). The fallback can be enabled
> > manually as well, by passing efi=old_map, but there is very little
> > evidence that suggests that this is something that is being relied
> > upon in the field.
> >
> > Given that UV1 support is not enabled by default by the distros
> > (Ubuntu, Fedora), there is no point in carrying this fallback code
> > all the time if there are no other users. So let's refactor it a bit
> > to make it depend on CONFIG_X86_UV, and remove the ability to enable
> > it by hand.
> >
> > Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> > Cc: Mike Travis <mike.travis@hpe.com>
> > Cc: Hedi Berriche <hedi.berriche@hpe.com>
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> 
> Boris, since you were the one that added efi=old_map: do you know of
> any cases beyond SGI UV1 where it was actually needed? There is some
> mention of using it to work around transient breakage on 32-bit caused
> by your original changes, but other than that, Google doesn't seem to
> know about any cases where efi=old_map is being used to deal with
> actual firmware quirks.
> 
> As a followup to this change, I'd like to move the old memmap handling
> into the UV1 support code, so it is omitted unless UV support is
> compiled it, and so it can be retired with the rest of it once that
> time comes.

Good idea.

So I remember "some apple laptops" but reading this again:

https://lore.kernel.org/patchwork/patch/704853/

looks like mfleming meant the opposite: some apple laptops don't like
the 1:1 runtime mapping. But there might be more and I believe mjg59 had
some use case at the time but I could be remembering it wrong.

Let me add them both to Cc for comment.

So one other reason for adding the =old_map thing is having a fallback
to the old method in case we break some boxes. It even says so in the
commit message of:

d2f7cbe7b26a ("x86/efi: Runtime services virtual mapping")

"While at it, add a chicken bit called "efi=old_map" which can be used
as a fallback to the old runtime services mapping method in case there's
some b0rkage with a particular EFI implementation..."

But I'm not aware of people still booting with "old_map" so I guess
deprecating it should be probably ok...

HTH.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Matthew Garrett]

On Tue, Dec 31, 2019 at 05:05:47PM +0100, Borislav Petkov wrote:

> looks like mfleming meant the opposite: some apple laptops don't like
> the 1:1 runtime mapping. But there might be more and I believe mjg59 had
> some use case at the time but I could be remembering it wrong.

I've lost most of the context for this over the years, I'm afraid. The 
case I remember was that the EFI reboot code on some hardware would 
attempt to access physical addresses and we wanted some form of 1:1 
mapping to handle that, but I really don't remember what the larger 
details were.

-- 
Matthew Garrett | mjg59@srcf.ucam.org

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Russ Anderson]

On Tue, Dec 31, 2019 at 05:05:47PM +0100, Borislav Petkov wrote:
> On Tue, Dec 31, 2019 at 12:13:18PM +0100, Ard Biesheuvel wrote:
> > (adding Boris and Dave for the historical perspective)
> > 
> > On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > We carry a quirk in the x86 EFI code to switch back to an older
> > > method of mapping the EFI runtime services memory regions, because
> > > it was deemed risky at the time to implement a new method without
> > > providing a fallback to the old method in case problems arose.
> > >
> > > Such problems did arise, but they appear to be limited to SGI UV1
> > > machines, and so these are the only ones for which the fallback gets
> > > enabled automatically (via a DMI quirk). The fallback can be enabled
> > > manually as well, by passing efi=old_map, but there is very little
> > > evidence that suggests that this is something that is being relied
> > > upon in the field.
> > >
> > > Given that UV1 support is not enabled by default by the distros
> > > (Ubuntu, Fedora), there is no point in carrying this fallback code
> > > all the time if there are no other users. So let's refactor it a bit
> > > to make it depend on CONFIG_X86_UV, and remove the ability to enable
> > > it by hand.
> > >
> > > Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> > > Cc: Mike Travis <mike.travis@hpe.com>
> > > Cc: Hedi Berriche <hedi.berriche@hpe.com>
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > 
> > Boris, since you were the one that added efi=old_map: do you know of
> > any cases beyond SGI UV1 where it was actually needed? There is some
> > mention of using it to work around transient breakage on 32-bit caused
> > by your original changes, but other than that, Google doesn't seem to
> > know about any cases where efi=old_map is being used to deal with
> > actual firmware quirks.

We (SGI -> HPE) have used the efi=old_map quirk to work around issues,
including on the currently shipping HPE Superdome Flex (aka UV4).

An example was working around an EFI locking issues when calling
into BIOS, fixed by this commit.

  f331e766c4be ("x86/platform/UV: Use efi_runtime_lock to serialise BIOS calls")

We do not currently use the quirk, and nopefully never will need to
use it again, but it has been used recently and are very glad Boris
added it.  I am hesitent to remove it because it has been used recently
on currently shipping hardware.

Thanks.

> > As a followup to this change, I'd like to move the old memmap handling
> > into the UV1 support code, so it is omitted unless UV support is
> > compiled it, and so it can be retired with the rest of it once that
> > time comes.
> 
> Good idea.
> 
> So I remember "some apple laptops" but reading this again:
> 
> https://lore.kernel.org/patchwork/patch/704853/
> 
> looks like mfleming meant the opposite: some apple laptops don't like
> the 1:1 runtime mapping. But there might be more and I believe mjg59 had
> some use case at the time but I could be remembering it wrong.
> 
> Let me add them both to Cc for comment.
> 
> So one other reason for adding the =old_map thing is having a fallback
> to the old method in case we break some boxes. It even says so in the
> commit message of:
> 
> d2f7cbe7b26a ("x86/efi: Runtime services virtual mapping")
> 
> "While at it, add a chicken bit called "efi=old_map" which can be used
> as a fallback to the old runtime services mapping method in case there's
> some b0rkage with a particular EFI implementation..."
> 
> But I'm not aware of people still booting with "old_map" so I guess
> deprecating it should be probably ok...
> 
> HTH.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

-- 
Russ Anderson,  SuperDome Flex Linux Kernel Group Manager
HPE - Hewlett Packard Enterprise (formerly SGI)  rja@hpe.com

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Ard Biesheuvel]

On Thu, 2 Jan 2020 at 15:38, Russ Anderson <rja@hpe.com> wrote:
>
> On Tue, Dec 31, 2019 at 05:05:47PM +0100, Borislav Petkov wrote:
> > On Tue, Dec 31, 2019 at 12:13:18PM +0100, Ard Biesheuvel wrote:
> > > (adding Boris and Dave for the historical perspective)
> > >
> > > On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
> > > >
> > > > We carry a quirk in the x86 EFI code to switch back to an older
> > > > method of mapping the EFI runtime services memory regions, because
> > > > it was deemed risky at the time to implement a new method without
> > > > providing a fallback to the old method in case problems arose.
> > > >
> > > > Such problems did arise, but they appear to be limited to SGI UV1
> > > > machines, and so these are the only ones for which the fallback gets
> > > > enabled automatically (via a DMI quirk). The fallback can be enabled
> > > > manually as well, by passing efi=old_map, but there is very little
> > > > evidence that suggests that this is something that is being relied
> > > > upon in the field.
> > > >
> > > > Given that UV1 support is not enabled by default by the distros
> > > > (Ubuntu, Fedora), there is no point in carrying this fallback code
> > > > all the time if there are no other users. So let's refactor it a bit
> > > > to make it depend on CONFIG_X86_UV, and remove the ability to enable
> > > > it by hand.
> > > >
> > > > Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> > > > Cc: Mike Travis <mike.travis@hpe.com>
> > > > Cc: Hedi Berriche <hedi.berriche@hpe.com>
> > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > >
> > > Boris, since you were the one that added efi=old_map: do you know of
> > > any cases beyond SGI UV1 where it was actually needed? There is some
> > > mention of using it to work around transient breakage on 32-bit caused
> > > by your original changes, but other than that, Google doesn't seem to
> > > know about any cases where efi=old_map is being used to deal with
> > > actual firmware quirks.
>
> We (SGI -> HPE) have used the efi=old_map quirk to work around issues,
> including on the currently shipping HPE Superdome Flex (aka UV4).
>
> An example was working around an EFI locking issues when calling
> into BIOS, fixed by this commit.
>
>   f331e766c4be ("x86/platform/UV: Use efi_runtime_lock to serialise BIOS calls")
>
> We do not currently use the quirk, and nopefully never will need to
> use it again, but it has been used recently and are very glad Boris
> added it.  I am hesitent to remove it because it has been used recently
> on currently shipping hardware.
>

Thanks for the data point.

So what about making it depend on CONFIG_X86_UV=y, would that still
work for you?

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Dimitri Sivanich]

On Thu, Jan 02, 2020 at 04:04:39PM +0100, Ard Biesheuvel wrote:
> On Thu, 2 Jan 2020 at 15:38, Russ Anderson <rja@hpe.com> wrote:
> >
> > On Tue, Dec 31, 2019 at 05:05:47PM +0100, Borislav Petkov wrote:
> > > On Tue, Dec 31, 2019 at 12:13:18PM +0100, Ard Biesheuvel wrote:
> > > > (adding Boris and Dave for the historical perspective)
> > > >
> > > > On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
> > > > >
> > > > > We carry a quirk in the x86 EFI code to switch back to an older
> > > > > method of mapping the EFI runtime services memory regions, because
> > > > > it was deemed risky at the time to implement a new method without
> > > > > providing a fallback to the old method in case problems arose.
> > > > >
> > > > > Such problems did arise, but they appear to be limited to SGI UV1
> > > > > machines, and so these are the only ones for which the fallback gets
> > > > > enabled automatically (via a DMI quirk). The fallback can be enabled
> > > > > manually as well, by passing efi=old_map, but there is very little
> > > > > evidence that suggests that this is something that is being relied
> > > > > upon in the field.
> > > > >
> > > > > Given that UV1 support is not enabled by default by the distros
> > > > > (Ubuntu, Fedora), there is no point in carrying this fallback code
> > > > > all the time if there are no other users. So let's refactor it a bit
> > > > > to make it depend on CONFIG_X86_UV, and remove the ability to enable
> > > > > it by hand.
> > > > >
> > > > > Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> > > > > Cc: Mike Travis <mike.travis@hpe.com>
> > > > > Cc: Hedi Berriche <hedi.berriche@hpe.com>
> > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > >
> > > > Boris, since you were the one that added efi=old_map: do you know of
> > > > any cases beyond SGI UV1 where it was actually needed? There is some
> > > > mention of using it to work around transient breakage on 32-bit caused
> > > > by your original changes, but other than that, Google doesn't seem to
> > > > know about any cases where efi=old_map is being used to deal with
> > > > actual firmware quirks.
> >
> > We (SGI -> HPE) have used the efi=old_map quirk to work around issues,
> > including on the currently shipping HPE Superdome Flex (aka UV4).
> >
> > An example was working around an EFI locking issues when calling
> > into BIOS, fixed by this commit.
> >
> >   f331e766c4be ("x86/platform/UV: Use efi_runtime_lock to serialise BIOS calls")
> >
> > We do not currently use the quirk, and nopefully never will need to
> > use it again, but it has been used recently and are very glad Boris
> > added it.  I am hesitent to remove it because it has been used recently
> > on currently shipping hardware.
> >
> 
> Thanks for the data point.
> 
> So what about making it depend on CONFIG_X86_UV=y, would that still
> work for you?

Yes, it will be sufficient to have it available with CONFIG_X86_UV=y.

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Russ Anderson]

On Thu, Jan 02, 2020 at 04:04:39PM +0100, Ard Biesheuvel wrote:
> On Thu, 2 Jan 2020 at 15:38, Russ Anderson <rja@hpe.com> wrote:
> >
> > On Tue, Dec 31, 2019 at 05:05:47PM +0100, Borislav Petkov wrote:
> > > On Tue, Dec 31, 2019 at 12:13:18PM +0100, Ard Biesheuvel wrote:
> > > > (adding Boris and Dave for the historical perspective)
> > > >
> > > > On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
> > > > >
> > > > > We carry a quirk in the x86 EFI code to switch back to an older
> > > > > method of mapping the EFI runtime services memory regions, because
> > > > > it was deemed risky at the time to implement a new method without
> > > > > providing a fallback to the old method in case problems arose.
> > > > >
> > > > > Such problems did arise, but they appear to be limited to SGI UV1
> > > > > machines, and so these are the only ones for which the fallback gets
> > > > > enabled automatically (via a DMI quirk). The fallback can be enabled
> > > > > manually as well, by passing efi=old_map, but there is very little
> > > > > evidence that suggests that this is something that is being relied
> > > > > upon in the field.
> > > > >
> > > > > Given that UV1 support is not enabled by default by the distros
> > > > > (Ubuntu, Fedora), there is no point in carrying this fallback code
> > > > > all the time if there are no other users. So let's refactor it a bit
> > > > > to make it depend on CONFIG_X86_UV, and remove the ability to enable
> > > > > it by hand.
> > > > >
> > > > > Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> > > > > Cc: Mike Travis <mike.travis@hpe.com>
> > > > > Cc: Hedi Berriche <hedi.berriche@hpe.com>
> > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > >
> > > > Boris, since you were the one that added efi=old_map: do you know of
> > > > any cases beyond SGI UV1 where it was actually needed? There is some
> > > > mention of using it to work around transient breakage on 32-bit caused
> > > > by your original changes, but other than that, Google doesn't seem to
> > > > know about any cases where efi=old_map is being used to deal with
> > > > actual firmware quirks.
> >
> > We (SGI -> HPE) have used the efi=old_map quirk to work around issues,
> > including on the currently shipping HPE Superdome Flex (aka UV4).
> >
> > An example was working around an EFI locking issues when calling
> > into BIOS, fixed by this commit.
> >
> >   f331e766c4be ("x86/platform/UV: Use efi_runtime_lock to serialise BIOS calls")
> >
> > We do not currently use the quirk, and nopefully never will need to
> > use it again, but it has been used recently and are very glad Boris
> > added it.  I am hesitent to remove it because it has been used recently
> > on currently shipping hardware.
> >
> 
> Thanks for the data point.
> 
> So what about making it depend on CONFIG_X86_UV=y, would that still
> work for you?

I want to make sure my undestanding of what you are proposing
is the same as what you are proposing.

I will have some additional background information shortly.

Thanks.
-- 
Russ Anderson,  SuperDome Flex Linux Kernel Group Manager
HPE - Hewlett Packard Enterprise (formerly SGI)  rja@hpe.com

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Ard Biesheuvel]

On Thu, 2 Jan 2020 at 17:45, Russ Anderson <rja@hpe.com> wrote:
>
> On Thu, Jan 02, 2020 at 04:04:39PM +0100, Ard Biesheuvel wrote:
> > On Thu, 2 Jan 2020 at 15:38, Russ Anderson <rja@hpe.com> wrote:
> > >
> > > On Tue, Dec 31, 2019 at 05:05:47PM +0100, Borislav Petkov wrote:
> > > > On Tue, Dec 31, 2019 at 12:13:18PM +0100, Ard Biesheuvel wrote:
> > > > > (adding Boris and Dave for the historical perspective)
> > > > >
> > > > > On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
> > > > > >
> > > > > > We carry a quirk in the x86 EFI code to switch back to an older
> > > > > > method of mapping the EFI runtime services memory regions, because
> > > > > > it was deemed risky at the time to implement a new method without
> > > > > > providing a fallback to the old method in case problems arose.
> > > > > >
> > > > > > Such problems did arise, but they appear to be limited to SGI UV1
> > > > > > machines, and so these are the only ones for which the fallback gets
> > > > > > enabled automatically (via a DMI quirk). The fallback can be enabled
> > > > > > manually as well, by passing efi=old_map, but there is very little
> > > > > > evidence that suggests that this is something that is being relied
> > > > > > upon in the field.
> > > > > >
> > > > > > Given that UV1 support is not enabled by default by the distros
> > > > > > (Ubuntu, Fedora), there is no point in carrying this fallback code
> > > > > > all the time if there are no other users. So let's refactor it a bit
> > > > > > to make it depend on CONFIG_X86_UV, and remove the ability to enable
> > > > > > it by hand.
> > > > > >
> > > > > > Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> > > > > > Cc: Mike Travis <mike.travis@hpe.com>
> > > > > > Cc: Hedi Berriche <hedi.berriche@hpe.com>
> > > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > > >
> > > > > Boris, since you were the one that added efi=old_map: do you know of
> > > > > any cases beyond SGI UV1 where it was actually needed? There is some
> > > > > mention of using it to work around transient breakage on 32-bit caused
> > > > > by your original changes, but other than that, Google doesn't seem to
> > > > > know about any cases where efi=old_map is being used to deal with
> > > > > actual firmware quirks.
> > >
> > > We (SGI -> HPE) have used the efi=old_map quirk to work around issues,
> > > including on the currently shipping HPE Superdome Flex (aka UV4).
> > >
> > > An example was working around an EFI locking issues when calling
> > > into BIOS, fixed by this commit.
> > >
> > >   f331e766c4be ("x86/platform/UV: Use efi_runtime_lock to serialise BIOS calls")
> > >
> > > We do not currently use the quirk, and nopefully never will need to
> > > use it again, but it has been used recently and are very glad Boris
> > > added it.  I am hesitent to remove it because it has been used recently
> > > on currently shipping hardware.
> > >
> >
> > Thanks for the data point.
> >
> > So what about making it depend on CONFIG_X86_UV=y, would that still
> > work for you?
>
> I want to make sure my undestanding of what you are proposing
> is the same as what you are proposing.
>

What I am proposing is to document efi=old_map as only being available
on kernels built with CONFIG_X86_UV=y, and moving the code that
implements it into the UV support code.

> I will have some additional background information shortly.
>

Thanks, that is very helpful.

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Russ Anderson]

On Thu, Jan 02, 2020 at 05:52:39PM +0100, Ard Biesheuvel wrote:
> On Thu, 2 Jan 2020 at 17:45, Russ Anderson <rja@hpe.com> wrote:
> >
> > I want to make sure my undestanding of what you are proposing
> > is the same as what you are proposing.
> >
> 
> What I am proposing is to document efi=old_map as only being available
> on kernels built with CONFIG_X86_UV=y, and moving the code that
> implements it into the UV support code.
> 
> > I will have some additional background information shortly.
> >
> 
> Thanks, that is very helpful.

After talking with some engineers, here is a brief history.

When EFI new mapping was implemented, it did not work with
the SGI UV1 bios, which worked with the old EFI mapping.
Boris added the efi=old_map quirk as a workaround to keep
UV1 working.

SGI UV2 bios (and later) have a fix for that issue, so the
quirk was modified for just UV1 by this commit.  That allowed
new EFI mapping to be used on newer UV platforms.

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/x86/platform/efi/quirks.c?id=d394f2d9d8e1e7b4959819344baf67b5995da9b0

There have been at least two other times efi=old_map has
been used to work around issues.

One was when KASLR was added (as part of the Spectre/Meldown
mitigation).  The initial implementation broke with new
map so efi=old_map was used as a workaround.  I don't know
if this was a distro specific breakage or upstream, but the
workaround limited the impact and the breakage was quickly
fixed.

Another time was the EFI locking issue mentioned earlier
in this thread.

Those are a couple of examples of efi=old_map being used
after the UV1 platform.  They were cases of issues that
impacted the new EFI mapping, not platform or bios issues,
and having the ability to fall back to the old EFI mapping
helped minimize the impact.  Neither were problems in the
new EFI mapping code itself, with the new mapping an
innocent victim of other issues.

Having the efi=old_map quirk available with CONFIG_X86_UV=y
makes it available on the platform I care about, and as it
is enabled in the distros we support (SLES, RHEL, Oracle Linux)
and Fedora.  Not sure if anyone else has used efi=old_map to
work around other issues, but this change would remove
old_map as a possible workaround for others.

Is there a compelling reason to put efi=old_map quirk
under CONFIG_X86_UV=y?  The original patch description assumed
only old SGI UV1 used efi=old_map, that it had not been
used on newer hardware, but that isn't the case.  It has been
used on newer currently shipping hardware.  Given that
new information is there a compelling reason for the change?

Thanks.

-- 
Russ Anderson,  SuperDome Flex Linux Kernel Group Manager
HPE - Hewlett Packard Enterprise (formerly SGI)  rja@hpe.com

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Ard Biesheuvel]

On Fri, 3 Jan 2020 at 00:13, Russ Anderson <rja@hpe.com> wrote:
>
> On Thu, Jan 02, 2020 at 05:52:39PM +0100, Ard Biesheuvel wrote:
> > On Thu, 2 Jan 2020 at 17:45, Russ Anderson <rja@hpe.com> wrote:
> > >
> > > I want to make sure my undestanding of what you are proposing
> > > is the same as what you are proposing.
> > >
> >
> > What I am proposing is to document efi=old_map as only being available
> > on kernels built with CONFIG_X86_UV=y, and moving the code that
> > implements it into the UV support code.
> >
> > > I will have some additional background information shortly.
> > >
> >
> > Thanks, that is very helpful.
>
> After talking with some engineers, here is a brief history.
>
> When EFI new mapping was implemented, it did not work with
> the SGI UV1 bios, which worked with the old EFI mapping.
> Boris added the efi=old_map quirk as a workaround to keep
> UV1 working.
>
> SGI UV2 bios (and later) have a fix for that issue, so the
> quirk was modified for just UV1 by this commit.  That allowed
> new EFI mapping to be used on newer UV platforms.
>
>   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/x86/platform/efi/quirks.c?id=d394f2d9d8e1e7b4959819344baf67b5995da9b0
>
> There have been at least two other times efi=old_map has
> been used to work around issues.
>
> One was when KASLR was added (as part of the Spectre/Meldown
> mitigation).  The initial implementation broke with new
> map so efi=old_map was used as a workaround.  I don't know
> if this was a distro specific breakage or upstream, but the
> workaround limited the impact and the breakage was quickly
> fixed.
>
> Another time was the EFI locking issue mentioned earlier
> in this thread.
>

So are you saying the distros updated their kernels which subsequently
broke your platforms, and you needed to use efi=old_map in production
to work around this? This sounds like something that should have been
caught in testing before the release was made.

Is there any way you could make one of these systems
available/accessible for testing new kernels? Also, was the breakage
related specifically to the use of the UV runtime services?

> Those are a couple of examples of efi=old_map being used
> after the UV1 platform.  They were cases of issues that
> impacted the new EFI mapping, not platform or bios issues,
> and having the ability to fall back to the old EFI mapping
> helped minimize the impact.  Neither were problems in the
> new EFI mapping code itself, with the new mapping an
> innocent victim of other issues.
>
> Having the efi=old_map quirk available with CONFIG_X86_UV=y
> makes it available on the platform I care about, and as it
> is enabled in the distros we support (SLES, RHEL, Oracle Linux)
> and Fedora.  Not sure if anyone else has used efi=old_map to
> work around other issues, but this change would remove
> old_map as a possible workaround for others.
>

Indeed.

> Is there a compelling reason to put efi=old_map quirk
> under CONFIG_X86_UV=y?  The original patch description assumed
> only old SGI UV1 used efi=old_map, that it had not been
> used on newer hardware, but that isn't the case.  It has been
> used on newer currently shipping hardware.  Given that
> new information is there a compelling reason for the change?
>

Every feature like this doubles the size of the validation matrix, and
so restricting efi=old_map to a single target helps to keep the
maintenance effort manageable.

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Russ Anderson]

On Fri, Jan 03, 2020 at 09:14:14AM +0100, Ard Biesheuvel wrote:
> On Fri, 3 Jan 2020 at 00:13, Russ Anderson <rja@hpe.com> wrote:
> > been used to work around issues.
> >
> > One was when KASLR was added (as part of the Spectre/Meldown
> > mitigation).  The initial implementation broke with new
> > map so efi=old_map was used as a workaround.  I don't know
> > if this was a distro specific breakage or upstream, but the
> > workaround limited the impact and the breakage was quickly
> > fixed.
> >
> > Another time was the EFI locking issue mentioned earlier
> > in this thread.
> >
> 
> So are you saying the distros updated their kernels which subsequently
> broke your platforms, and you needed to use efi=old_map in production
> to work around this? This sounds like something that should have been
> caught in testing before the release was made.

The Spectre/Meldown change was rushed through, without proper
testing.  The lesson was that even security fixes need full testing.
All involved (that I am aware of) do not want to repeat releasing
code that has not been fully tested.

The EFI locking issue was caught by the HPE BRT (Basic Regression Test)
team, but after it had been released by distros.  It was a small
timing hole that ALMOST always worked, which is why it was not detected
immediately.

> Is there any way you could make one of these systems
> available/accessible for testing new kernels? Also, was the breakage
> related specifically to the use of the UV runtime services?

HPE does have systems at Red Hat and SUSE (part of the distro test
environments), along with internal test systems.  HPE does have access
to pre-release distro (RHEL, SLES, Oracle Linux) kernels, including
nightly development builds.  I have a kernel engineer on-site at Red Hat
with access to RH kernel engineers and git trees.  We do test upstream
kernels and have fixed regressions.  That said, we do have limited
resources (test systems, people, time) and do as much as we can with
what we have, so it is not perfect.  But we try our best to be perfect.

> > Is there a compelling reason to put efi=old_map quirk
> > under CONFIG_X86_UV=y?  The original patch description assumed
> > only old SGI UV1 used efi=old_map, that it had not been
> > used on newer hardware, but that isn't the case.  It has been
> > used on newer currently shipping hardware.  Given that
> > new information is there a compelling reason for the change?
> 
> Every feature like this doubles the size of the validation matrix, and
> so restricting efi=old_map to a single target helps to keep the
> maintenance effort manageable.

Understood.  

Thanks.
-- 
Russ Anderson,  SuperDome Flex Linux Kernel Group Manager
HPE - Hewlett Packard Enterprise (formerly SGI)  rja@hpe.com

Re: [RFC PATCH] efi/x86: limit EFI old memory map to SGI UV1 machines

[Dave Young]

Mistakenly dropped cc list, add again.
On 01/01/20 at 11:04am, Dave Young wrote:
> Hi Ard,
> On 12/31/19 at 12:13pm, Ard Biesheuvel wrote:
> > (adding Boris and Dave for the historical perspective)
> > 
> > On Thu, 26 Dec 2019 at 10:55, Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > We carry a quirk in the x86 EFI code to switch back to an older
> > > method of mapping the EFI runtime services memory regions, because
> > > it was deemed risky at the time to implement a new method without
> > > providing a fallback to the old method in case problems arose.
> > >
> > > Such problems did arise, but they appear to be limited to SGI UV1
> > > machines, and so these are the only ones for which the fallback gets
> > > enabled automatically (via a DMI quirk). The fallback can be enabled
> > > manually as well, by passing efi=old_map, but there is very little
> > > evidence that suggests that this is something that is being relied
> > > upon in the field.
> > >
> > > Given that UV1 support is not enabled by default by the distros
> > > (Ubuntu, Fedora), there is no point in carrying this fallback code
> > > all the time if there are no other users. So let's refactor it a bit
> > > to make it depend on CONFIG_X86_UV, and remove the ability to enable
> > > it by hand.
> > >
> > > Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> > > Cc: Mike Travis <mike.travis@hpe.com>
> > > Cc: Hedi Berriche <hedi.berriche@hpe.com>
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > 
> > Boris, since you were the one that added efi=old_map: do you know of
> > any cases beyond SGI UV1 where it was actually needed? There is some
> > mention of using it to work around transient breakage on 32-bit caused
> > by your original changes, but other than that, Google doesn't seem to
> > know about any cases where efi=old_map is being used to deal with
> > actual firmware quirks.
> > 
> > As a followup to this change, I'd like to move the old memmap handling
> > into the UV1 support code, so it is omitted unless UV support is
> > compiled it, and so it can be retired with the rest of it once that
> > time comes.
> > 
> 
> I also only know about the SGI UV1 quirk, and I'm not sure about
> if this affects some 32bit user, otherwise it should be a good idea
> As for the 32bit I remember Sai previously did use old_map for kexecing.
> Added Sai in cc for thoughts.
> 
> Thanks
> Dave