[xen staging] ns16550: MMIO r/o ranges are maintained at page granularity

[patchbot@xxxxxxx]

commit 82de0a6facf8e4699958654bcbef974e33480ed7
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Sep 7 09:36:59 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Sep 7 09:36:59 2021 +0200

    ns16550: MMIO r/o ranges are maintained at page granularity
    
    Passing byte granular values will not have the intended effect. Address
    the immediate issue, but I don't think what we do is actually
    sufficient: At least some devices allow access to their registers via
    either I/O ports or MMIO. In such aliasing cases we'd need to protect
    the MMIO range even when we use I/O port accesses to drive the port.
    
    Note that this way we may write-protect MMIO ranges of unrelated devices
    as well. To deal with this, faults resulting from this would need
    handling, to emulate the accesses outside of the protected range. (An
    alternative would be to relocate the BAR, but I'm afraid this might end
    up even more challenging.)
    
    Fixes: c9f8e0aee507 ("ns16550: Add support for UART present in Broadcom 
TruManage capable NetXtreme chips")
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 xen/drivers/char/ns16550.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index e2c24082c3..30596d60d4 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -421,8 +421,8 @@ static void __init ns16550_init_postirq(struct serial_port 
*port)
     if ( uart->bar || uart->ps_bdf_enable )
     {
         if ( uart->param && uart->param->mmio &&
-             rangeset_add_range(mmio_ro_ranges, uart->io_base,
-                                uart->io_base + uart->io_size - 1) )
+             rangeset_add_range(mmio_ro_ranges, PFN_DOWN(uart->io_base),
+                                PFN_UP(uart->io_base + uart->io_size) - 1) )
             printk(XENLOG_INFO "Error while adding MMIO range of device to 
mmio_ro_ranges\n");
 
         if ( pci_ro_device(0, uart->ps_bdf[0],
--
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