efi/earlycon: Remap entire framebuffer after page initialization

When the commit 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation") moved x86 specific EFI earlyprintk implementation to shared location it also tweaked the behaviour. In particular it dropped a trick with full framebuffer remapping after page initialization. This led to two regressions:
1) very slow scrolling after page initialization;
2) kernel hang when keep_bootcon parameter is being provided.

Returning the trick back fixes #2 and mitigates, i.e. reduces the window when slowness appears, #1 presumably due to eliminating heavy map()/unmap() operations per each pixel line on the screen.

Fixes 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation")

Cc Ard Biesheuvel <[email protected]>

Cc Alexander Graf <[email protected]>

Cc Matt Fleming <[email protected]>

Signed-off-by Andy Shevchenko <[email protected]>

---
v2:
- add __exitcall()
- swap type and attribute for __init / __exit functions as most used in the kernel

 drivers/firmware/efi/earlycon.c | 34 +++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

drivers/firmware/efi/earlycon.c +34 -0

index c9a0efca17b0..8c6a3c67b7f2 100644
@@ -17,14 +17,48 @@ static const struct font_desc *font;
 static u32 efi_x, efi_y;
 static u64 fb_base;
 static pgprot_t fb_prot;
+static void *efi_fb;
+
+/*
+ * efi earlycon needs to use early_memremap() to map the framebuffer.
+ * But early_memremap() is not usable for 'earlycon=efifb keep_bootcon',
+ * memremap() should be used instead. memremap() will be available after
+ * paging_init() which is earlier than initcall callbacks. Thus adding this
+ * early initcall function early_efi_map_fb() to map the whole efi framebuffer.
+ */
+static int __init early_efi_map_fb(void)
+{
+	u32 size;
+
+	size = screen_info.lfb_size;
+	if (pgprot_val(fb_prot) == pgprot_val(PAGE_KERNEL))
+		efi_fb = memremap(fb_base, size, MEMREMAP_WB);
+	else
+		efi_fb = memremap(fb_base, size, MEMREMAP_WC);
+
+	return efi_fb ? 0 : -ENOMEM;
+}
+early_initcall(early_efi_map_fb);
+
+static void __exit early_efi_unmap_fb(void)
+{
+	memunmap(efi_fb);
+}
+__exitcall(early_efi_unmap_fb);
 
 static __ref void *efi_earlycon_map(unsigned long start, unsigned long len)
 {
+	if (efi_fb)
+		return efi_fb + start;
+
 	return early_memremap_prot(fb_base + start, len, pgprot_val(fb_prot));
 }
 
 static __ref void efi_earlycon_unmap(void *addr, unsigned long len)
 {
+	if (efi_fb)
+		return;
+
 	early_memunmap(addr, len);
 }
 

Signature · 1 line

2.24.0

Quoted 8 lines · Andy Shevchenko

When the commit 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation") moved x86 specific EFI earlyprintk implementation to shared location it also tweaked the behaviour. In particular it dropped a trick with full framebuffer remapping after page initialization. This led to two regressions:
1) very slow scrolling after page initialization;
2) kernel hang when keep_bootcon parameter is being provided.

Quoted 3 lines

Returning the trick back fixes #2 and mitigates, i.e. reduces the window when slowness appears, #1 presumably due to eliminating heavy map()/unmap() operations per each pixel line on the screen.

Please, hold on. I found an issue when no earlycon is not being provided in command line. I will fix, test and send a v3 soon.

Quoted 67 lines

Fixes 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation")

Cc Ard Biesheuvel <[email protected]>

Cc Alexander Graf <[email protected]>

Cc Matt Fleming <[email protected]>

Signed-off-by Andy Shevchenko <[email protected]>

---
v2:
- add __exitcall()
- swap type and attribute for __init / __exit functions as most used in the kernel

 drivers/firmware/efi/earlycon.c | 34 +++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

drivers/firmware/efi/earlycon.c +34 -1

index c9a0efca17b0..8c6a3c67b7f2 100644
@@ -17,14 +17,48 @@ static const struct font_desc *font;
 static u32 efi_x, efi_y;
 static u64 fb_base;
 static pgprot_t fb_prot;
+static void *efi_fb;
+
+/*
+ * efi earlycon needs to use early_memremap() to map the framebuffer.
+ * But early_memremap() is not usable for 'earlycon=efifb keep_bootcon',
+ * memremap() should be used instead. memremap() will be available after
+ * paging_init() which is earlier than initcall callbacks. Thus adding this
+ * early initcall function early_efi_map_fb() to map the whole efi framebuffer.
+ */
+static int __init early_efi_map_fb(void)
+{
+     u32 size;
+
+     size = screen_info.lfb_size;
+     if (pgprot_val(fb_prot) == pgprot_val(PAGE_KERNEL))
+             efi_fb = memremap(fb_base, size, MEMREMAP_WB);
+     else
+             efi_fb = memremap(fb_base, size, MEMREMAP_WC);
+
+     return efi_fb ? 0 : -ENOMEM;
+}
+early_initcall(early_efi_map_fb);
+
+static void __exit early_efi_unmap_fb(void)
+{
+     memunmap(efi_fb);
+}
+__exitcall(early_efi_unmap_fb);
 
 static __ref void *efi_earlycon_map(unsigned long start, unsigned long len)
 {
+     if (efi_fb)
+             return efi_fb + start;
+
      return early_memremap_prot(fb_base + start, len, pgprot_val(fb_prot));
 }
 
 static __ref void efi_earlycon_unmap(void *addr, unsigned long len)
 {
+     if (efi_fb)
+             return;
+
      early_memunmap(addr, len);
 }
 
--

Quoted 2 lines

2.24.0

--
With Best Regards,
Andy Shevchenko