[PATCH 5.4 072/222] efi/earlycon: Fix write-combine mapping on x86

Greg Kroah-Hartman
2020-01-22T13:21:05Z

From: Arvind Sankar <nivedita@alum.mit.edu>

commit d92b54570d24d017d2630e314b525ed792f5aa6c upstream.

On x86, until PAT is initialized, WC translates into UC-. Since we
calculate and store pgprot_writecombine(PAGE_KERNEL) when earlycon is
initialized, this means we actually use UC- mappings instead of WC
mappings, which makes scrolling very slow.

Instead store a boolean flag to indicate whether we want to use
writeback or write-combine mappings, and recalculate the actual pgprot_t
we need on every mapping. Once PAT is initialized, we will start using
write-combine mappings, which speeds up the scrolling considerably.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Fixes: 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation")
Link: https://lkml.kernel.org/r/20191224132909.102540-2-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/firmware/efi/earlycon.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

--- a/drivers/firmware/efi/earlycon.c
+++ b/drivers/firmware/efi/earlycon.c
@@ -17,7 +17,7 @@ static const struct console *earlycon_co
static const struct font_desc *font;
static u32 efi_x, efi_y;
static u64 fb_base;
-static pgprot_t fb_prot;
+static bool fb_wb;
static void *efi_fb;

/*
@@ -33,10 +33,8 @@ static int __init efi_earlycon_remap_fb(
if (!earlycon_console || !(earlycon_console->flags & CON_ENABLED))
return 0;

- if (pgprot_val(fb_prot) == pgprot_val(PAGE_KERNEL))
- efi_fb = memremap(fb_base, screen_info.lfb_size, MEMREMAP_WB);
- else
- efi_fb = memremap(fb_base, screen_info.lfb_size, MEMREMAP_WC);
+ efi_fb = memremap(fb_base, screen_info.lfb_size,
+ fb_wb ? MEMREMAP_WB : MEMREMAP_WC);

return efi_fb ? 0 : -ENOMEM;
}
@@ -53,9 +51,12 @@ late_initcall(efi_earlycon_unmap_fb);

static __ref void *efi_earlycon_map(unsigned long start, unsigned long len)
{
+ pgprot_t fb_prot;
+
if (efi_fb)
return efi_fb + start;

+ fb_prot = fb_wb ? PAGE_KERNEL : pgprot_writecombine(PAGE_KERNEL);
return early_memremap_prot(fb_base + start, len, pgprot_val(fb_prot));
}

@@ -215,10 +216,7 @@ static int __init efi_earlycon_setup(str
if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
fb_base |= (u64)screen_info.ext_lfb_base << 32;

- if (opt && !strcmp(opt, "ram"))
- fb_prot = PAGE_KERNEL;
- else
- fb_prot = pgprot_writecombine(PAGE_KERNEL);
+ fb_wb = opt && !strcmp(opt, "ram");

si = &screen_info;
xres = si->lfb_width;